Serena Williams from the U.S. celebrates a point on her way to win the final of the Madrid Open tennis tournament against Maria Sharapova from Russia, in Madrid Sunday, May 12, 2013. (AP Photo/Daniel Ochoa de Olza)
Serena Williams from the U.S. celebrates a point on her way to win the final of the Madrid Open tennis tournament against Maria Sharapova from Russia, in Madrid Sunday, May 12, 2013. (AP Photo/Daniel Ochoa de Olza)
Maria Sharapova, of Russia, makes a return against Caroline Wozniacki, of Denmark, during their match at the BNP Paribas Open tennis tournament on Sunday, March 17, 2013, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)
Maria Sharapova, of Russia, makes a return against Caroline Wozniacki, of Denmark, during their match at the BNP Paribas Open tennis tournament on Sunday, March 17, 2013, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)
Russia's Maria Sharapova celebrates after defeating Venus Williams of the U.S. in their third round match at the Australian Open tennis championship in Melbourne, Australia, Friday, Jan. 18, 2013. (AP Photo/Dita Alangkara)
Russia's Maria Sharapova celebrates after defeating Venus Williams of the U.S. in their third round match at the Australian Open tennis championship in Melbourne, Australia, Friday, Jan. 18, 2013. (AP Photo/Dita Alangkara)
Victoria Azarenka, of Belarus, blows kisses to the crowd after her match against Maria Sharapova, of Russia, during a semifinal match at the 2012 US Open tennis tournament, Friday, Sept. 7, 2012, in New York. Coming all the way back from a set and a break down, the top-seeded Azarenka prevailed in a stirring third, beating four-time major champion Sharapova 3-6, 6-2, 6-4 to reach her first U.S. Open final. (AP Photo/Charles Krupa)
Victoria Azarenka, of Belarus, blows kisses to the crowd after her match against Maria Sharapova, of Russia, during a semifinal match at the 2012 US Open tennis tournament, Friday, Sept. 7, 2012, in New York. Coming all the way back from a set and a break down, the top-seeded Azarenka prevailed in a stirring third, beating four-time major champion Sharapova 3-6, 6-2, 6-4 to reach her first U.S. Open final. (AP Photo/Charles Krupa)
Russia's Maria Sharapova celebrates during her match with Marion Bartoli, of France, in the quarterfinals during the 2012 US Open tennis tournament, Wednesday, Sept. 5, 2012, in New York. (AP Photo/Darron Cummings)
