Victoria Azarenka, Novak Djokovic and Andy Murray in action
Novak Djokovic, of Serbia, celebrates after defeating Andy Murray, of Britain, 7-6 (1), 6-7 (1), 6-2, 6-4 in the quarterfinals of the U.S. Open tennis tournament Thursday, Sept. 4, 2014, in New York.DARRON CUMMINGS/The Associated Press
Andy Murray returns a shot to Novak Djokovic, of Serbia, during the quarterfinals of the U.S. Open tennis tournament Wednesday, Sept. 3, 2014, in New York.Darron Cummings/The Associated Press
Novak Djokovic, of Serbia, reacts during a match against Andy Murray, of Britain, during the quarterfinals of the U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.John Minchillo/The Associated Press
Serena Williams of the U.S. reacts after winning a women’s singles quarterfinals match against Flavia Pennetta of Italy in Arthur Ashe Stadium at the U.S. Open tennis tournament in New York, Sept. 3, 2014. Williams defeated Pennetta 6-3, 6-2.Barton Silverman/The New York Times
Victoria Azarenka, of Belarus, returns a shot against Ekaterina Makarova, of Russia, during the quarter-finals of the 2014 U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.Mike Groll/The Associated Press
Ekaterina Makarova, of Russia, returns a shot against Victoria Azarenka, of Belarus, during the quarter-finals of the 2014 U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.Mike Groll/The Associated Press
Ekaterina Makarova, of Russia, follows through on a shot against Victoria Azarenka, of Belarus, during the quarter-finals of the 2014 U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.Mike Groll/The Associated Press
Victoria Azarenka, of Belarus, talks to the chair umpire after a decision at the net during the quarter-finals against Ekaterina Makarova, of Russia, during the 2014 U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.Julio Cortez/The Associated Press
Ekaterina Makarova of Russia serves to Victoria Azarenka of Belarus during their quarter-final match at the 2014 U.S. Open tennis tournament in New York, September 3, 2014.MIKE SEGAR/Reuters
Victoria Azarenka, of Belarus, reacts after a shot against Ekaterina Makarova, of Russia, during the quarter-finals of the 2014 U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.Mike Groll/The Associated Press
Victoria Azarenka, of Belarus, right, and Ekaterina Makarova, of Russia, walk back to their benches between games during the quarter-finals of the 2014 U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.Julio Cortez/The Associated Press
Kei Nishikori, of Japan, returns a shot again Stan Wawrinka, of Switzerland, during the quarter-finals of the 2014 U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.Mike Groll/The Associated Press
Stan Wawrinka, of Switzerland, prepares to serve against Kei Nishikori, of Japan, during the quarterfinals of the 2014 U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.Julio Cortez/The Associated Press
Stan Wawrinka, of Switzerland, serves against Kei Nishikori, of Japan, during the quarterfinals of the 2014 U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.Julio Cortez/The Associated Press
Stan Wawrinka, of Switzerland, prepares to serve against Kei Nishikori, of Japan, during the quarterfinals of the 2014 U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.Mike Groll/The Associated Press
Kei Nishikori, of Japan, returns a shot against Stan Wawrinka, of Switzerland, during the quarterfinals of the 2014 U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.Mike Groll/The Associated Press
Kei Nishikori of Japan hits a return to Stan Wawrinka of Switzerland during their quarter-final match at the 2014 U.S. Open tennis tournament in New York, September 3, 2014.EDUARDO MUNOZ/Reuters
Stan Wawrinka of Switzerland hits a return to Kei Nishikori of Japan during their quarter-final match at the 2014 U.S. Open tennis tournament in New York, September 3, 2014.EDUARDO MUNOZ/Reuters
Spectators watch play between Kei Nishikori, of Japan, and Stan Wawrinka, of Switzerland, during the quarter-finals of the 2014 U.S. Open tennis tournament, Wednesday, Sept. 3, 2014, in New York.Julio Cortez/The Associated Press