Caroline Wozniacki, of Denmark, reacts after defeating Maria Sharapova, of Russia, during the fourth round of the 2014 U.S. Open tennis tournament, Sunday, Aug. 31, 2014, in New York. (AP Photo/Kathy Willens)
Serena Williams returns to Caroline Wozniacki, from Denmark, during a semifinal match at the Western & Southern Open tennis tournament, Saturday, Aug. 16, 2014, in Mason, Ohio. (AP Photo/David Kohl)
Denmark's Caroline Wozniacki wipes her face during the first round match of the French Open tennis tournament against Belgium's Yanina Wickmayer at the Roland Garros stadium, in Paris, France, Tuesday, May 27, 2014. (AP Photo/Darko Vojinovic)
Belgium's Yanina Wickmayer celebrates winning the first round match of the French Open tennis tournament against Denmark's Caroline Wozniacki at the Roland Garros stadium, in Paris, France, Tuesday, May 27, 2014. (AP Photo/Darko Vojinovic)
Denmark's Caroline Wozniacki, left, shakes hands with Belgium's Yanina Wickmayer after losing the first round match of the French Open tennis tournament at the Roland Garros stadium, in Paris, France, Tuesday, May 27, 2014. (AP Photo/Darko Vojinovic)
Belgium's Yanina Wickmayer celebrates scoring a point during the first round match of the French Open tennis tournament against Denmark's Caroline Wozniacki at the Roland Garros stadium, in Paris, France, Tuesday, May 27, 2014. (AP Photo/Darko Vojinovic)
Denmark's Caroline Wozniacki returns the ball during the first round match of the French Open tennis tournament against Belgium's Yanina Wickmayer at the Roland Garros stadium, in Paris, France, Tuesday, May 27, 2014. (AP Photo/Darko Vojinovic)