In 1993, at age 17, Sugiyama played tennis legend Martina Navratilova in her native city, losing in three sets. The same year, she made her Grand Slam debut at Wimbledon but lost in the first round to world number 30 Gigi Fernández in three sets. In 1994, Sugiyama again reached the main draw at Wimbledon but lost in her first round to world number six and compatriot Kimiko Date. Later that year she reached her first singles final in Surabaya but was forced to retire against Elena Wagner. She went on to win the Japan Open doubles at Tokyo, her first tour title. Later that year, she broke into the WTA Top 100. In 1995, she won her first Grand Slam match and reached the 4th round of Roland Garros. In the first round, the Japanese player defeated 15th-seeded Grand Slam runner-up and former Top-5 player Helena Suková by 9–7 in the final set, her first victory over a Top-20 player. Two months after, she defeated Amanda Coetzer to reach the third round, while losing to world number four and former Wimbledon champion Conchita Martínez. In November, she made an impressive run at the Oakland Tier II tournament. While she was only ranked 63, she defeated 22nd-ranked Irina Spîrlea, former Wimbledon runner-up Zina Garrison Jackson, and number ten Lindsay Davenport to reach the second final of her career, where she lost to number seven Magdalena Maleeva. Because of this, Sugiyama broke into the Top 50.
In 1996, she reached the third round at the Australian Open. In Miami, seeded 23rd, Sugiyama reached the fourth round, defeating number ten Jana Novotná, her second Top-10 victory. That moved her into the Top-30. She also reached the semifinals of the Japan Open in Tokyo and the 4th round at Wimbledon, where she defeated number five Anke Huber, her third Top-10 and first Top-5 victory. She represented Japan and reached the 3rd round at the Atlanta Olympics defeating Martina Hingis.
In 1997, Sugiyama began her season by playing her third finals match, losing to Elena Likhovtseva, after defeating Sabine Appelmans in the quarter final. The following week she reached the 2nd round at the Australian Open. In April, she won her first professional title at the Japan Open in Tokyo against Amy Frazier. However, she could not reach a good result in Grand Slam events, with a 2nd round exit at the French Open and US Open and a first round loss at Wimbledon. At the end of the year, she reached her first Tier I final at the Kremlin Cup in Moscow, defeating Natasha Zvereva, number 14 Brenda Schultz-McCarthy, number 9 and multi-Grand Slam events winner Arantxa Sánchez Vicario, Dominique Van Roost before failing in the final against first seed and 2nd-ranked Jana Novotná.
In 1998, she opened with a second singles title in Gold Coast. Then she broke into the WTA Top-20 and reached another semifinal in Sydney, defeating Conchita Martínez. Throughout that year, Sugiyama showed consistency: a third WTA Tour title at the Japan Open, quarterfinals in Tokyo (Pan Pacific), Berlin, defeating number 4 Amanda Coetzer, playing Strasbourg and San Diego, defeating Steffi Graf, Luxembourg, third round in Indian Wells, Miami and Montreal and second round at both French and US Open. In 1999, she reached the final at the Japan Open, the semifinals in Gold Coast and Tokyo (Princess Cup) defeating number 8 Julie Halard-Decugis, the quarterfinals in Strasbourg and Moscow, defeating number 6 Mary Pierce, 3rd in Indian Wells, Montreal, defeating number 7 Jana Novotná and at the US Open. She also reached the second round at the French Open and Wimbledon. The same year, Sugiyama won the US Open mixed doubles with Mahesh Bhupathi (India), her first Grand Slam title.
On July 10 Sugiyama reached the final of the Women's Doubles at Wimbledon, partnered by Julie Halard-Decugis, but lost in straight sets to sisters Venus and Serena Williams 6–3 6–2 after a one-day rain delay. On September 10 Sugiyama won the Women's Doubles at the US Open, defeating Cara Black of Zimbabwe and Russian Elena Likhovtseva 6–0 1–6 6–1 in one hour and 19 minutes. On October 23 she became the first Japanese woman to rank number one in the world in doubles, winning seven titles in the process.
Sugiyama's greatest success was Scottsdale 2003. Beating Lindsay Davenport in the second round, Ai went on to defeat Eleni Daniilidou to progress to the semifinals. Scheduling problems forced both the semifinals and finals matches—for both singles and doubles—to be played on the Sunday of the tournament. Thus in a single day, Ai managed to save a matchpoint in the semifinals against Alexandra Stevenson, rally from a set down to defeat doubles partner Kim Clijsters in the final, and then secure victories in both doubles matches to raise both trophies. The year 2003 proved to be her best year ever, pushing Serena Williams to the limit at Roland Garros and reaching the round of 16 in Wimbledon and US Open where her fourth round loss to Francesca Schiavone at Flushing Meadows was rather controversial. She finished the year ranked tenth, having defeated world number one Justine Henin in the round robin section of the season-ending championships. She also won a total of 8 doubles titles that year: 7 with Kim Clijsters (Sydney, Antwerp, Scottsdale, Roland Garros, Wimbledon, San Diego, Zurich) and 1 with Liezel Huber (Linz).
Sugiyama began 2005 with four consecutive first-round losses. She lost in the first rounds of the first three Grand Slams; only at San Diego did she really do well, making it to the final, which she lost 0–6 3–6 to Mary Pierce, having defeated Daniela Hantuchová, Sesil Karantacheva and Svetlana Kuznetsova en route. Sugiyama also reached the final in doubles with Hantuchová, losing to Virginia Ruano-Pascual and Conchita Martínez. She broke her Grand Slam "curse", reaching the third round before losing to Clijsters, the eventual champion.
That year, Ai had better results in doubles than in singles. Partnering with Elena Dementieva, she reached the finals of her first tournament, Sydney, losing to Bryanne Stewart/Samantha Stosur. They reached the Round of 16 at the Australian Open. She entered a few tournaments with Anastasia Myskina and Elena Likhovtseva, but with poor results. In Berlin, she played again with Daniela Hantuchová, reaching the Semifinal, losing to Black and Huber. At the French, they lost to Birnerová and Vanc in the second round. They won their next tournament, in Birmingham over Daniilidou and Russel 6–2 6–3. At Wimbledon, Hantuchová and Sugiyama reached the Quarterfinal, losing to eventual champions Black and Huber. At the Canadian Open in Toronto, they lost the semifinal to eventual champions Grönefeld and Navratilova. At the US Open, they reached the third round, losing to Zi Yan and Zheng Jie. Ai tried three partners in the next tournaments, before returning to Daniela in Zurich, where they reached the finals (beating top seeds Lisa Raymond and Stosur en route), losing a close match to Black and Rennae Stubbs, 6–7(6) 7–6(4) 6–3. They finished the year ranked #5, failing to qualify for the Year-End Championships.
Sugiyama played mixed doubles at two events: the French & the US Open. At Roland Garros, playing with Mirnyi, she lost in the first round. At the US Open, she partnered with Ullyett. The duo reached the quarterfinals, losing to eventual champions Hantuchová and Bhupathi. Entering the Doha with an 0–5 singles record, she managed to beat wildcard Selima Sfar 6–3 6–3. In the second round, she surprisingly upset (4) Myskina 7–6(2) 6–7(6) 6–4, needing several match points to close the match out. In her quarterfinal match against Julia Schruff, she had a comfortable 6–3 6–2 win. She lost in the semifinal, in an epic match against Nadia Petrova, 6–1 7–6 (2). At 0–4 in the second, she won five consecutive games to 5–4. She won the doubles title with Hantuchová, defeating Yan and Zheng in the semifinal 6–3 3–6 6–3, and Ting Li and Tiantian Sun 6–4 6–4 in the final.
In Rome 2006 she and Hantuchová won the title, their third as a team and biggest title, beating Li and Sun 6–4 6–1; Black and Stubbs (2) 6–4 6–0, and Květa Peschke and Schiavone (8) 3–6 6–3 6–1.
At the French Open, 22nd seeded Ai beat Daniilidou 6–7 6–0 6–3 in the first round, but lost to French qualifier Aravane Rezaï 4–6 6–4 6–3. Deciding not to compete in the mixed, Ai and Daniella beat Caroline Dhenin and Mathilde Johansson 6–4 6–3, then squashed Sofia Arvidsson and Martina Müller 6–1 6–1; they escaped from Marion Bartoli and Shahar Pe'er, 1–6 7–6(3) 6–2. In the quarterfinals, they beat second-seeded Black and Stubbs 6–1 7–6(5). In the semifinals, they beat fourth-seeded Yan and Zheng 6–3 3–6 6–3. They lost 6–3 6–2 in the final to top-seeded Raymond and Stosur.
Wimbledon 2006 saw Sugiyama, the eighteenth seed, defeat 12th seed, Martina Hingis, 7–5 3–6 6–4 to advance to the fourth round.
The summer brought several bad singles losses, as well as doubles upsets. Sugiyama reached the final in Los Angeles, bowing to Ruano Pascual and Paola Suárez. In Montréal, she beat Aleksandra Wozniak and Anabel Medina Garrigues before losing to Kuznetsova. In doubles, partnering with Nathalie Dechy, they reached the quarterfinals.
The US Open arrived, and, seeded twenty-eighth, she defeated Zuzana Ondrášková, Tathiana Garbin before falling to second seed Justine Henin 4–6 6–1 6–0.
In Beijing, she beat qualifier Alicia Molik, who was also her doubles partner in the event, in the first round, 6–2 7–6. She then upset fourth-seeded Nicole Vaidišová 6–4 1–6 6–3 before losing to Peng Shuai in another three-set match 6–7 6–3 6–2. She reached the final of a Tier IV event in Seoul, losing to Eleni Daniilidou of Greece in three sets, 3–6 6–2 6–7.
The beginning of 2007 was better than the prior two years. She lost to Anastasiya Yakimova in the second round of the Australian Open (10–8 in the third), before beating her in Miami. Sugiyama and Daniela Hantuchová reached the quarterfinals, losing to eventual champions Black and Huber. In Tokyo, she reached the quarterfinals, losing to number one Maria Sharapova 4–6, 6–1, 6–0. In Doha, she injured her toe, but recovered to reach the round of 16 in Indian Wells.
In Miami, she fell to Dinara Safina in the third. She went 0–3 in Fed Cup play versus France, losing to both Tatiana Golovin and Dechy, but rebounded to win 50k Gifu with Ayumi Morita. The Japanese duo lost only one set en route to the title. She played in Berlin with Katarina Srebotnik. They swept Lourdez Domínguez Lino and Flavia Pennetta 6–0, 6–0, but then fell to the second seeded Black and Huber 0–6, 6–4, [10–7] the same day.
Her next tournament was Rome, where she beat Maria Kirilenko in 2 hours 49 minutes 6–4, 5–7, 7–5. She lost to Pe'er 6–0, 6–2 in the next round. At Roland Garros, she reached the third round. She defeated Eva Birnerová 6–3, 6–4 in the first round and Meilen Tu 6–3, 1–6, 6–1 in the second round, but then fell to Anna Chakvetadze, the ninth seed, 6-4m 6–4. In doubles, seeded seventh with Srebotnik, she defeated Lucie Hradecká and Renata Voráčová 6–7, 7–5, 6–2 in the first round, Stéphanie Foretz and Camille Pin 6–1, 6–3 in the second round, and Pe'er and Safina 6–1, 6–2 in the third round. They then defeated Maria Elena Camerin and Gisela Dulko 4–6, 7–5, 6–3 in the quarterfinals. They upset top seeds and defending champions Raymond and Stosur in the semifinals, winning 1–6, 6–4, 6–3 to reach the French Open finals. They lost in the final to Alicia Molik and Mara Santangelo 7–6, 6–4.
At Wimbledon, seeded 26th, she beat wildcard Melanie South 6–3, 6–2 and Alizé Cornet 4–6, 6–0, 6–3. She lost 6–3, 6–3 against the second seeded Sharapova in the third round. In doubles, she and Srebotnik beat Andreea Ehritt-Vanc and Anastassia Rodionova 4–6, 6–3, 6–2; Émilie Loit and Nicole Pratt 6–0, 6–3, and got a walkover from Bartoli and Meilen Tu in the third round. In the quarterfinals, they beat Elena Likhovtseva and Sun Tiantian 6–4, 7–6 (5). They came back from 1–6, 0–3 to beat top-seeded Raymond and Stosur, winning 1–6, 6–3, 6–2. They lost in the final to the second seeded Black and Huber 3–6, 6–3, 6–2.
During the U.S. Open Series, she reached the third round of San Diego, where she defeated Sybille Bammer 6–2, 7–6. She then lost to Chakvetadze 6–4, 6–4. She reached two doubles semifinals in San Diego and Stanford with Srebotnik, losing both times to Victoria Azarenka and Chakvetadze. However, they won Toronto, defeating Peng Shuai and Yan 6–1, 7–5 in the quarterfinal, Molik and Santangelo 6–2, 6–3 in the semifinal and Black and Huber 6–4, 2–6, [10–5] in the final, winning their first title as a team.
At the 2007 US Open, Sugiyama lost in the second round to Ekaterina Makarova. Ai and Srebotnik impressively defeated Sun Shengnan and Ji Chunmei 6–0, 6–1, and eventually defeated Michaëlla Krajicek and Agnieszka Radwańska 5–7, 6–0, 6–2. The team advanced to the quarterfinals after defeating Loit and Vania King 6–3, 6–2, but lost to eventual champions Dechy and Safina 7–5, 6–3.
Srebotnik and Sugiyama continued their form and thus qualified for the 2007 WTA Tour Championships, which were held in Madrid. The team, seeded second, defeated the Taiwanese duo of Chan Yung-jan and Chuang Chia-jung 6–2, 6–2, but lost to Black and Huber in the final 5–7, 6–3, [10–8].
In singles, Sugiyama's season started out badly, as she lost to Azarenka in Gold Coast and Gajdosova in Sydney. However, in Melbourne, her form returned, beating Vera Zvonareva 6–3, 1–1 ret. in the first round and Tatiana Perebiynis 6–4 6–4 in the second round, before losing to 12th seed Vaidišová, 6–3 6–4. In doubles, she and Srebotnik lost in straight sets in Sydney to Yan/Zheng, the eventual champions. In Melbourne, they drew the Williams sisters in the second round and lost 6–2 7–6. Sugiyama's dream of a career slam died.
In doubles, she reached the final in Antwerp with Peschke, as well as the semifinals in Doha and Dubai with Srebotnik.
On March 30 in the third round at the Tier I event in Miami, she upset 8th seeded Hantuchová 6–4, 6–7(8), 7–5 in an epic match. She came back after losing a match point in the second set, as well as having served for the match twice in the second set. In the third set, she was down three to none, but still managed to win. It was her first top ten win since Beijing 2006. In the next round, she lost to Zvonareva 2–6 7–6(5) 0–6. In doubles, she and Srebotnik won the title, beating Akiko Morigami and Alina Jidkova 6–4 6–3, Lucie Hradecká and Renata Voráčová 6–4 6–3, and Davenport and Hantuchová 6–4 3–6 [10–4]. They earned the title by beating Australian runners-up Azarenka and Pe'er 6–0 6–3, and number one team Black and Huber 7–5 4–6 [10–3]. It was their second team title, and Sugiyama's 8th Tier I title.
Sugiyama won her 9th Tier I doubles title with Srebotnik at Charleston at the Family Circle cup, their third team title, scoring 6–2, 6–2 over Edina Gallovits-Hall and Olga Govortsova.
Sugiyama broke the record for consecutive slam appearances woman with 57 as of her appearance in the 2008 Wimbledon tournament. Sugiyama made it to the third round of Ladies' Singles, losing to Alisa Kleybanova of Russia, 6–4, 6–4.
At Stanford, she defeated Alexa Glatch 6–2, 3–6, 7–5, and then crushed world number 11 Hantuchová 6–3, 6–1. In the quarters she beat Dominika Cibulková 6–7, 7–6, 6–3, saving 3 match points in the process.
Sugiyama and Ayumi Morita represented their nation at the 2008 Summer Olympics, losing in the second round to the Williams'.
Ai started with a first round loss to Stosur, and in the women's doubles a semi-final finish losing to Klaudia Jans and Alicja Rosolska in the Brisbane International partnering Hantuchová. In the Medibank International, Sugiyama made the semi-finals eventually losing to Safina 6–4, 7–6(3)
In the 2009 Australian Open, Ai made the third round losing to Jelena Janković 6–4, 6–4. As the 9th seed in doubles playing with Hantuchová, they beat the #1 seeds Black and Huber 6–7(0), 6–3, 7–6(10). In the third set "Hantuyama" were down 5–2, but rallied to take it to a tie-break, where they saved seven match points to win 12–10. In the semi-finals, they beat Dechy and Santangelo 6–4, 6–2 to make it her first women's doubles final there. They were defeated by the Williams in two sets, 6–3, 6–3. A respiratory infection forced her to withdraw from the 2009 Open GDF Suez. Sugiyama entered the 2009 Dubai Tennis Championships and lost in the opening round to Bartoli in a tight 3-set match 0–6, 6–4, 6–7(6). Sugiyama and Hantuchová also played doubles but withdrew because of the infection.
At the 2009 BNP Paribas Open Sugiyama and Hantuchová were seeded 5 in the women's doubles but lost to the pair Alla Kudryavtseva and Rodionova 6–4, 4–6, 16–14 in the first round. In singles, she lost to qualifier Angela Haynes in the second round 4–6, 5–7.
At the Sony Ericsson open she lost her opening matches in singles and doubles, being beaten in the second round in singles after receiving a bye. Her loss in the doubles event with Hantuchová dropped her doubles ranking to number 5.
Sugiyama lost four consecutive singles matches in Miami, Stuttgart, Rome, and Madrid. However alongside Hantuchová, Sugiyama made the finals at the Rome Masters where they lost to the number 7 seeds, Su-Wei Hsieh and Peng. They reached the quarter finals at the 2009 Madrid Masters where they lost to Stosur and Stubbs, whom she and Akgul Amanmuradova beat in the finals at Eastbourne, her 38th doubles title.
On June 22 she extended her record of consecutive Grand Slam appearances to 61 at Wimbledon, defeating the seeded Patty Schnyder in straight sets 6–4 6–4 to break her 11 match losing streak. She lost in the third round to Hantuchová.
In Stanford she lost to Sharapova in three sets 4–6, 7–6, 1–6, saving two match points in the second set. She then lost in the second round in Los Angeles to Radwańska 6–2, 6–0.
Sugiyama retired at the end of the 2009 tennis season after the 2009 Toray Pan Pacific Open, held in her native country, Japan. A special ceremony for her was held at center court before the tournament. Ai planned a few months at home before concentrating on teaching youngsters at her tennis academy in Japan.2009: Australian Open, Rome, Tokyo (w. Hantuchová)
2008: Antwerp (w. Peschke)
2007: Wimbledon, Roland Garros, Linz, WTA Tour Championships (w. Srebotnik)
2006: Roland Garros, Los Angeles (w. Hantuchová)
2005: Sydney (w. Dementieva), San Diego, Zurich (w. Hantuchová)
2004: Wimbledon (w. Huber), Olympics (lost bronze medal match with Asagoe)
2003: Berlin, Indian Wells, Tours Championships (all w. Clijsters), Shanghai (w. Tanasugarn)
2002: San Diego, Los Angeles (both w. Hantuchová), Montréal (Canadian Open), Shanghai, Linz (all w. Fujiwara)
2001: Wimbledon, Tokyo (both w. Clijsters)
2000: Wimbledon, Montréal (Canadian Open), Linz (all w. Halard-Decugis)
1999: Paris, Leipzig (both w. Likhovtseva)
1997: Strasbourg (w. Likhovtseva)
1995: Tokyo (w. Nagatsuka)
1994: Surabaya (w. Nagatsuka)
A = did not participate in the tournament
SR = the ratio of the number of singles tournaments won to the number of those tournaments played
LQ = lost in the qualifying tournament