Rasmus Festersen signed his first professional contract with Danish club Silkeborg IF who had invited him to try out for the team during the off season in the summer of 2007. Silkeborg manager Peder Knudsen said about Festersen: "Rasmus has done very well during the daily training and in friendly matches. We hope that he can develop his game even more as a full time professional player, because he is undoubtedly a very exciting type. He is real "football-smart" and has some great offensive qualities.
Festersen got his debut on his 21st birthday 26 August 2007 against Frem. He came on as a substitute in the 10th minute of the game replacing the injured Kim Olsen. Silkeborg won 3-2 and Festersen made a promising first appearance with an assist to fellow striker Simon Azoulay Pedersen goal, just six minutes after he went on the pitch.
On September 5, 2007 Festersen scored his first goal for the club helping Silkeborg to a 2-0 win against FC Svendborg in the Danish Cup.
During his brief time at Silkeborg IF Festersen drew attention to himself as the fastest player in the squad., but eventually he failed to become a regular starter. After only six months at the club, he moved to lower ranking Slagelse B&I in January 2008, becoming one of the first signings after the club's newly set ambitions of returning to the top of Danish football within six years.
Festersen immediately became a big success scoring nine goals in 15 games in the spring of 2008 helping his club to a take fifth position in the 2nd Division East.
In the 2008/09 season he scored 20 goals for the club, which had then changed their name to FC Vestsjælland. FC Vestsjælland won promotion to the Danish 1st Division, with Festersen honored as the 2nd Division East Player of the Year.
In January 2010 Festersen signed a new contract with FC Vestsjælland committing himself to the club until the summer of 2012.
In April 2012 Rasmus Festersen and FC Vestsjælland announced that he would be leaving the club after the season to pursue a footballing career and to study in Australia. Later revealed that he will be playing for Oakleigh Cannons FC.
On November 6, 2011 Rasmus Festersen was the centre of a bizarre red card during a match between FC Vestsjælland and Viborg FF. Festersen scored the first goal of the match and celebrated it by holding up a mask in front of his face. Having already been booked earlier in the match Festersen was then, to his own and the teammates' big surprise, shown a second yellow card and sent off.
After the match Festersen explained that the celebration was meant as a salute to some friends at home, but that he regretted his actions, as it gave the referee the chance to give him a second booking.
FC Vestsjælland's manager Ove Pedersen however showed support to his player and said: "I don't understand it. It's a ridiculous rule.". Eventually Festersen received one match suspension for his red card.
Following the red card Festersen was often referred as 'Zorro' in the Danish media, suggesting that the mask he wore was an imitation of the fictional character "Zorro".
A similar sending off happened to Brazilian footballer Neymar, who was also sent off for putting on a mask during a Copa Libertadores match.
Alongside his career as a professional football player Rasmus Festersen is studying for a degree in Business and Geography at Roskilde University near Copenhagen. In an interview Festersen said: "I choose to study, because I believe that you can use your mind for education and your legs playing soccer. Combining the two helps me stimulate my intellectual side as well as my physical needs, which eventually makes me become a better human being.".2009 Promotion from Danish Second Division East
2009 Player for the year Danish Second Division East