The 1975 World Chess Championship was never played due to a dispute over the match format. Champion Bobby Fischer (United States) was to play Anatoly Karpov (Soviet Union) in Manila, commencing June 1, 1975. However, he refused to play the then-standard "Best of 24 games" match, and after FIDE were unable to work out a compromise, forfeited his title instead. Karpov was named World Champion by default on April 3, 1975.
Two 18 player, single round robin Interzonals were played with the top three from each qualifying for the Candidates Tournament. Leningrad and Petropolis, Brazil were the venues.
Korchnoi, Karpov, and Byrne qualified for the Candidates Tournament.
Mecking qualified outright for the Candidates Tournament, while the three players tied for second place contested a playoff in Portoroz for the remaining two spots.
Portisch and Polugaevsky qualified.
The 1974 Candidates Tournament was played as knockout matches. Spassky as the loser of the last championship match and Petrosian as loser of the previous candidates final were seeded directly into the tournament and joined by the top three from each of the two interzonals.
The first round matches were first to win three games, draws not counting. Semifinals were first to four wins, while the final was first to five wins but with a maximum of 24 games. Karpov beat Korchnoi 3-2 with 19 draws, earning the right to challenge Fischer.
The semifinal stage was marked by the presence of two ex-champions, Petrosian and Spassky, playing in different matches. The two had faced each other in the 1966 and 1969 title matches. Both were eliminated in this stage of the current cycle. Although the match rules called for four wins in the semifinals, Petrosian resigned the match after losing three games. He then attempted, through political means, to have the result of the match reversed.
Fischer had, prior to his 1972 match against Spassky, felt that the first-to-12½-points format was not fair, since it encouraged whoever was leading to play for draws instead of wins. He himself espoused this strategy in the match: after having taken a comfortable lead, he drew games 14–20. With each game, he coasted closer to the title, while Spassky lost a chance to fight back. This style of chess offended Fischer. Instead he demanded the format be changed to that used in the very first World Championship, between Wilhelm Steinitz and Johannes Zukertort, where the winner was the first player to score 10 wins with draws not counting. In case of a 9–9 score, the champion would retain title, and the prize fund split equally. A FIDE Congress was held in 1974 during the Nice Olympiad. The delegates voted in favor of Fischer's 10-win proposal, but rejected the 9–9 clause as well as the possibility of an unlimited match. In response, Fischer refused to defend his title. Deadlines were extended for Fischer's reconsideration, but he did not respond, so Karpov was named World Champion by default on April 3, 1975.
After Fischer defaulted, Karpov became World Champion by forfeit. Whether Karpov could have beaten Fischer is a matter of speculation. Future world champion Garry Kasparov argued that Karpov would have had good chances, because he had beaten Spassky convincingly and was a new breed of tough professional, and indeed had higher quality games, while Fischer had been inactive for three years. Spassky thought that Fischer would have won in 1975 but Karpov would have qualified again and beaten Fischer in 1978.
The manner in which he became champion was a monkey Karpov carried on his back for the rest of his career. He combated this by participating in nearly every major tournament for the next ten years. He convincingly won the very strong Milan tournament in 1975, and captured his first of three Soviet titles in 1976. He created a phenomenal streak of tournament wins against the strongest players in the world. Karpov held the record for most consecutive tournament victories (nine) until it was shattered by Garry Kasparov (14). As a result, most chess professionals eventually agreed that Karpov is a legitimate world champion.
Karpov is on record saying that if he had had the opportunity to play Fischer for the crown in his twenties, he could have been a much better player as a result.