Venus Williams, of the United States, leaps after defeating Samantha Stosur, from Australia, 6-2, 6-7 (2), 6-4, during a quarterfinal at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. (AP Photo/Al Behrman)

Serena Williams, of the United States, reacts after missing a point against Angelique Kerber, from Germany, during a quarterfinal at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. Kerber won 6-4, 6-4. (AP Photo/Al Behrman)

Samantha Stosur, from Australia, serves against Venus Williams during a quarterfinals match at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. (AP Photo/Al Behrman)

Serena Williams reacts after missing a point against Angelique Kerber, from Germany, during a quarterfinal at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. Kerber won 6-4, 6-4. (AP Photo/Al Behrman)

Roger Federer, from Switzerland, serves against Mardy Fish during a quarterfinal at the Western & Southern Open tennis tournament on Friday, Aug. 17, 2012, in Mason, Ohio. (AP Photo/Al Behrman)

Novak Djokovic, from Serbia, hits a backhand shot against Marin Cilic, from Croatia, during a quarterfinals match at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. Djokovic won 6-3, 6-2. (AP Photo/Al Behrman)

PGA champion Rory McIlroy, left, watches a match between Caroline Wozniacki, from Denmark, and Anastasia Pavlyuchenkova, from Russia, at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. Pavlyuchenkova won 6-4, 6-4. (AP Photo/Al Behrman)

Caroline Wozniacki, from Denmark, walks back to the baseline after missing a shot against Anastasia Pavlyuchenkova, from Russia, during a match at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. Pavlyuchenkova won 6-4, 6-4. (AP Photo/Al Behrman)

Venus Williams returns a serve against Samantha Stosur, from Australia, during a quarterfinals match at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. (AP Photo/Al Behrman)

Samantha Stosur, from Australia, hits a backhand shot against Venus Williams during a quarterfinals match at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. (AP Photo/Al Behrman)

Marin Cilic, from Croatia, hits a forehand shot against Novak Djokovic, from Serbia, during a quarterfinals match at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. Djokovic won 6-3, 6-2. (AP Photo/Al Behrman)

Serena Williams returns a serve against Angelique Kerber, from Germany, during a quarterfinal at the Western & Southern Open tennis tournament on Friday, Aug. 17, 2012, in Mason, Ohio. Kerber won 6-4, 6-4. (AP Photo/Al Behrman)

Milos Raonic, of Canada, serves to Stanislas Wawrinka, of Switzerland, during a quarterfinal at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. (AP Photo/Al Behrman)

Angelique Kerber, from Germany, acknowledges the crowd after defeating Serena Williams 6-4, 6-4 in a quarterfinal at the Western & Southern Open tennis tournament on Friday, Aug. 17, 2012, in Mason, Ohio. (AP Photo/Al Behrman)

Mardy Fish hits a forehand against Roger Federer, from Switzerland, during a quarterfinal at the Western & Southern Open tennis tournament on Friday, Aug. 17, 2012, in Mason, Ohio. (AP Photo/Al Behrman)

Roger Federer, from Switzerland, hits a forehand against Mardy Fish during a quarterfinal at the Western & Southern Open tennis tournament on Friday, Aug. 17, 2012, in Mason, Ohio. (AP Photo/Al Behrman)

Roger Federer, from Switzerland, returns to Mardy Fish, of the United States, during a quarterfinal at the Western & Southern Open tennis tournament, Friday, Aug. 17, 2012, in Mason, Ohio. (AP Photo/Al Behrman)

FILE - In this Aug. 17, 2012, file photo, Novak Djokovic, from Serbia, hits a backhand shot against Marin Cilic, from Croatia, during a quarterfinals 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)