Defending champions Victoria Azarenka of Belarus and Serbia's Novak Djokovic pose with their trophies prior to the the official draw of the Australian Open tennis championship in Melbourne Australia, Friday, Jan. 10, 2014. (AP Photo/Mark Baker)
Juan Martin del Potro of Argentina plays a shot in his quarterfinals match against Radek Stepanek of the Czech Republic during the Sydney International tennis tournament in Sydney, Australia, Thursday, Jan. 9, 2014. (AP Photo/Rob Griffith)
Defending champions Victoria Azarenka of Belarus and Serbia's Novak Djokovic walk with their trophies prior to the the official draw of the Australian Open tennis championship in Melbourne Australia, Friday, Jan. 10, 2014. (AP Photo/Mark Baker)
Serbia's Novak Djokovic signs autographs for fans following his exhibition match against Juan Monaco of Argentina at the Kooyong Classic ahead of the Australian Open tennis championship in Melbourne Australia, Thursday, Jan. 9, 2014. (AP Photo/Joshua Baker)
Defending champions Victoria Azarenka of Belarus and Serbia's Novak Djokovic pose with their trophies prior to the official draw of the Australian Open tennis championship in Melbourne Australia, Friday, Jan. 10, 2014. (AP Photo/Aijaz Rahi)