Roger Federer, from Switzerland, hits a return against Stanislas Wawrinka, from Switzerland, during a semifinals match at the Western & Southern Open tennis tournament, Saturday, Aug. 18, 2012, in Mason, Ohio. Federer won 7-6 (4), 6-3. (AP Photo/Al Behrman)

Roger Federer, from Switzerland, clinches his fist after winning a game against Stanislas Wawrinka, from Switzerland, during a semifinal match at the Western & Southern Open tennis tournament, Saturday, Aug. 18, 2012, in Mason, Ohio. (AP Photo/Al Behrman)

FILE - In this Aug. 18, 2012, file photo, Roger Federer, from Switzerland, reaches for a shot against Stanislas Wawrinka, from Switzerland, during a semifinals match at the Western & Southern Open tennis tournament in Mason, Ohio. In an Olympic year, the U.S. Open _ scheduled to begin on Monday, Aug. 27, and considered the toughest test in tennis even under normal circumstances _ is essentially the season's fifth major, causing many top players to double down on their fitness and reorganize their schedules to prepare for what they hope will be a two-week grind in the fishbowl that is Flushing Meadows. (AP Photo/Al Behrman, File)