Germany's Philipp Kohlschreiber plays a shot against John Isner of the US during their 2012 US Open men's third round singles match at the USTA Billie Jean King National Tennis Center in New York on September 3, 2012.

John Isner of the USA reacts to a lost point in the fourth set against Phillip Kohlschreiber of Germany during Day Seven of the 2012 US Open.

Novak Djokovic of Serbia returns a shot during his men's singles third round match against Julien Benneteau of France on Day Seven of the 2012 US Open.

John Isner of the USA returns a shot to Phillip Kohlschreiber of Germany during Day Seven of the 2012 US Open.

Nadia Petrova of Russia celebrates serves against Maria Sharapova of Russia during Day Seven of the 2012 U.S. Open.

Novak Djokovic of Serbia (2) after winning against Julien Benneteau of France (31) during their 2012 US Open men's singles match.

Maria Sharapova of Russia celebrates her match win over Nadia Petrova of Russia during Day Seven of the 2012 US Open.

Petra Kvitova of the Czech Republic hits a return to Marion Bartoli of France during their women's singles fourth round match at the 2012 US Open tennis tournament. Bartoli won 1-6, 6-2, 6-0.

Samantha Stosur of Australia returns a shot during her women's singles fourth round match against Laura Robson of Great Britain on Day Seven of the 2012 US Open.

David Ferrer of Spain hits a return to Lleyton Hewitt of Australia during their men's singles match at the 2012 US Open tennis tournament on September 2, 2012 in New York.

Victoria Azarenka of Belarus plays a shot against Anna Tatishvili of Georgia during their 2012 US Open women's singles third round match at the USTA Billie Jean King National Tennis Center in New York.

Richard Gasquet of France hits a return to Steve Johnson of the US during their men's singles third round match at the 2012 US Open tennis tournament. Gasquet won 7-6 (7/4), 6-2, 6-3.

Andy Roddick of the United States shakes hands with Fabio Fognini of Italy after their men's singles third round match on Day Seven of the 2012 US Open.

Colin Fleming smashes the ball next to his partner Ross Hutchins of Great Britain during their men's doubles third round match against Ryan Harrison and Christian Harrison of the United States on Day Seven of the 2012 US Open.

Ryan (Left) and Christian Harrison of the United States tap hands during their men's doubles third round match against Colin Fleming and Ross Hutchins of Great Britain on Day Seven of the 2012 US Open.

Novak Djokovic of Serbia reacts after winning his men's singles third round match against Julien Benneteau of France on Day Seven of the 2012 US Open.