London Olympics | Tennis

A weary Roger Federer of Switzerland leans on the net during a lengthy third set against Argentina’s Juan Martin del Potro. The match lasted nearly five hours.   (Robert Gauthier / Los Angeles Times)

Roger Federer of Switzerland clenches his fist in victory after beating Argentina’s Juan Martin del Potro on center court at Wimbledon. The match lasted almost five hours and was the longest in Olympic history.   (Robert Gauthier / Los Angeles Times)

Juan Martin del Potro, right, and Roger Federer embrace after the men’s singles semifinals.  (Martin Bernetti / AFP / Getty Images)

Juan Martin del Potro of Argentina suffers a cramp midway through a marathon tennis match against Switerland’s Roger Federer.   (Robert Gauthier / Los Angeles Times)

Roger Federer of Switzerland celebrates a point against Argentina’s Juan Martin del Potro.   (Robert Gauthier / Los Angeles Times)

Juan Martin del Potro crumbles in pain at the net after losing a point to Roger Federer of Switzerland.  (Robert Gauthier / Los Angeles Times)

Juan Martin del Potro flattens the ball with a big forehand return to Roger Federer during their three-set match in the semifinals of the London Olympics.  (Elise Amendola / Associated Press)

Roger Federer strikes ball during his three-set victory over Juan Martin del Potro on Friday.  (Clive Brunskill / Getty Images)

Serena Williams of the United States smashes a forehand against Victoria Azarenka of Belarus in the women’s tennis singles semifinal. Williams won and will move to the finals to face Russia’s Maria Sharapova.  (Clive Brunskill / Getty Images)

Russia’s Maria Sharapova celebrates her victory over fellow countrywoman Maria Kirilenko in their women’s singles tennis semifinal match on Friday at the London Olympics. Sharapova will play Serena Williams in the gold-medal match.  (Luis Acosta / AFP / Getty Images)

Maria Sharapova tries to track down a shot by Maria Kirilenko during their semifinal match at the All England Lawn and Tennis Club on Friday at Wimbledon.  (Mark Humphrey / Associated Press)