Guangzhou WTA Tour in Guangzhou (AP Photo, File)

French Open tennis, Roland Garros stadium, Paris (AP Photo/Michel Euler, File)

Australian Open Grand Slam, Melbourne (ANSA/FRANCIS MALASIG)

Australian Open tennis, Melbourne (Photo by Greg WOOD / AFP)

Australian Open Grand Slam, Melbourne (ANSA/FRANCIS MALASIG)

Madrid Open ( REUTERS/Susana Vera/File Photo)

Madrid Open ( REUTERS/Susana Vera/File Photo)

Australian Open - Melbourne Park, Melbourne, Australia (REUTERS/Adnan Abidi/File Photo)

Australian Open - Melbourne Park, Melbourne, Australia (REUTERS/Kim Hong-Ji/File Photo)

Australian Open (REUTERS/Edgar Su/File Photo/File Photo)

French Open, Roland Garros stadium, in Paris (AP Photo/Michel Euler, File)

Australian Open tennis, Melbourne (Photo by WILLIAM WEST / AFP)

China Open tennis, Beijing (Photo by Fred DUFOUR / AFP)

Wimbledon Championships at The All England Lawn Tennis Club in Wimbledon (Photo by ADRIAN DENNIS / AFP) / RESTRICTED TO EDITORIAL USE

Australian Open, Melbourne (Photo by Jewel SAMAD / AFP)

China Open tennis,Beijing (Photo by GREG BAKER / AFP)

China Open tennis, Beijing (Photo by GREG BAKER / AFP)

China Open tennis, Beijing (Photo by GREG BAKER / AFP)

Australian Open, Melbourne (Photo by William WEST / AFP)

The Roland Garros French Open, Paris (Photo by Eric Feferberg / AFP)

WTA Tianjin Open, Tianjin (Photo by AFP)

Guangzhou WTA Tour in Guangzhou (AP Photo, File)