Roger Federer will play Juan Martin del Potro in the Olympic semifinals. He beat American John Isner, 6-4, 7-6 (5) in the quarterfinals on Centre Court at Wimbledon on Thursday. Federer has 17 Grand Slam titles and won an Olympic gold medal in doubles in 2008, but has never won an Olympic medal in singles. Novak Djokovic plays Andy Murray in the other semifinal.
