Serena Williams reacts after losing a point to Maria Sharapova, of Russia, at the Sony Open Tennis tournament in Key Biscayne, Fla., Thursday, March 27, 2014. (AP Photo/Alan Diaz)
Novak Djokovic, of Serbia, pumps his fist after winning 7-5, 6-3 against Andy Murray, of Britain, at the Sony Open Tennis tournament in Key Biscayne, Fla., Wednesday, March 26, 2014. (AP Photo/Alan Diaz)
Kei Nishikori of Japan, returns a shot from Roger Federer of Switzerland, at the Sony Open Tennis tournament, Wednesday, March 26, 2014 in Key Biscayne, Fla. (AP Photo/Wilfredo Lee)
Kei Nishikori of Japan, serves to Roger Federer of Switzerland, at the Sony Open Tennis tournament, Wednesday, March 26, 2014 in Key Biscayne, Fla. (AP Photo/Wilfredo Lee)
Roger Federer of Switzerland, returns a shot from Kei Nishikori of Japan, at the Sony Open Tennis tournament, Wednesday, March 26, 2014 in Key Biscayne, Fla. (AP Photo/Wilfredo Lee)
Li Na of China, serves to Caroline Wozniacki of Denmark, at the Sony Open Tennis tournament, Wednesday, March 26, 2014 in Key Biscayne, Fla. (AP Photo/Wilfredo Lee)