US Davis Cup tennis player John Isner reacts after he defeated Swiss Davis Cup player Roger Federer during a Davis Cup World Group first-round second match between Switzerland and the US in the Forum Arena in Fribourg, Switzerland, Friday, Feb. 10, 2012. (AP Photo/Keystone/Laurent Gillieron)
Rafael Nadal (left) celebrates a point win against Roger Federer during their semifinal Jan. 26, 2012, at the Australian Open in Melbourne, Australia. (Associated Press)
Novak Djokovic reacts after ousting Roger Federer in the U.S. Open semifinals Saturday and improving to 63-2 in 2011. (Associated Press)
Novak Djokovic reacts after winning a semifinal match against Roger Federer at the U.S. Open tennis tournament in New York on Saturday, Sept. 10, 2011. (AP Photo/Charles Krupa)
Roger Federer has a 223-33 record in Grand Slam matches, an .871 winning percentage. He faces Santiago Giraldo of Colombia on Monday.
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12th-seeded Jo-Wilfried Tsonga celebrates after defeating Roger Federer. Tsonga will Novak Djokovic, who is 46-1 this season, in the semifinals Friday.
Roger Federer leaves the court after his bid for a seventh Wimbledon championship and 17th Grand slam title ended in the quarterfinals.
France's Jo-Wilfried Tsonga (left), consoles Switzerland's Roger Federer after defeating him in their match at the All England Lawn Tennis Championships at Wimbledon on June 29, 2011. (Associated Press)
Switzerland's Roger Federer celebrates defeating Argentina's David Nalbandian in their match at the All England Lawn Tennis Championships at Wimbledon, Saturday, June 25, 2011. (AP Photo/Anja Niedringhaus)
Rafael Nadal lifts his trophy after defeating Switzerland's Roger Federer (right) in the men's final match of the French Open tennis tournament at the Roland Garros Stadium in Paris on Sunday, June 5, 2011. (AP Photo/Lionel Cironneau)
Spain's Rafael Nadal reacts after defeating Switzerland's Roger Federer during the men's final match for the French Open tennis tournament at the Roland Garros stadium, Sunday, June 5, 2011, in Paris. (AP Photo/Lionel Cironneau)
Switzerland's Roger Federer reacts as he plays Serbia's Novak Djokovic during their semi final match for the French Open tennis tournament at the Roland Garros stadium in Paris, Friday June 3, 2011. Federer won 7-6, 6-3, 3-6, 7-6.(AP Photo/Michel Euler)
Roger Federer of Switzerland celebrates his victory over Gael Monfils of France in the quarter final match of the French Open tennis tournament in Roland Garros stadium in Paris, Tuesday May 31, 2011. Federer won the match in three sets 6-4, 6-3, 6-7. (AP Photo/Michel Euler)
Roger Federer, a 16-time major champion, defeated Stanislas Wawrinka 6-3, 6-2, 7-5 at Roland Garros to reach the quarterfinals at a record 28th Grand Slam tournament in a row. (Associated Press)
Tennis player Roger Federer from Switzerland talks to journalists a day ahead of Dubai ATP Tennis Championships in Dubai, United Arab Emirates, Sunday, Feb. 20, 2011. (AP Photo/Kamran Jebreili)
Serbia's Novak Djokovic raises his arms as he celebrates his win over Switzerland's Roger Federer in their semifinal at the Australian Open tennis championships in Melbourne, Australia, on Thursday, Jan. 27, 2011. (AP Photo/Mark Baker)
FOR SPANISH END OF THE YEAR STORY 2010 TENNIS - FILE - In this Nov. 28, 2010 file photo Switzerland's Roger Federer celebrates as he holds the trophy after beating Spain's Rafael Nadal, left, to win the singles final tennis match at the ATP World Tour Finals at the O2 Arena in London. (AP Photo/Kirsty Wigglesworth, File)
Roger Federer of Switzerland returns the ball to Richard Gasquet of France during their match of the Paris Tennis Masters tournament, Wednesday, Nov. 10, 2010. (AP Photo/Lionel Cironneau)
Switzerland's Roger Federer kisses the cup during the award ceremony after his final match against Serbia's Novak Djokovic at the Davidoff Swiss Indoors tennis tournament at the St. Jakobshalle in Basel, Switzerland, Sunday, Nov. 7, 2010. (AP Photo/Keystone, Ennio Leanza)
Tennis players Roger Federer, left, and Rafael Nadal look on during Arthur Ashe Kids Day at the USTA Billie Jean King National Tennis Center on Saturday, Aug. 28, 2010 in New York. (AP Photo/Evan Agostini)