Serena Williams of the United States waves to the crowd after defeating Vesna Dolonc of Serbia in their second round match at the Australian Open tennis championship in Melbourne, Australia, Wednesday, Jan. 15, 2014.(AP Photo/Aaron Favila)
Serena Williams of the United States reacts after losing a point to Vesna Dolonc of Serbia during their second round match at the Australian Open tennis championship in Melbourne, Australia, Wednesday, Jan. 15, 2014.(AP Photo/Aaron Favila)
Novak Djokovic of Serbia makes a forehand return to Leonardo Mayer of Argentina during their second round match at the Australian Open tennis championship in Melbourne, Australia, Wednesday, Jan. 15, 2014.(AP Photo/Aaron Favila)
Novak Djokovic of Serbia signs autographs after winning his second round match against Leonardo Mayer of Argentina at the Australian Open tennis championship in Melbourne, Australia, Wednesday, Jan. 15, 2014.(AP Photo/Aaron Favila)
Novak Djokovic of Serbia waves to the crowd after winning his second round match against Leonardo Mayer of Argentina at the Australian Open tennis championship in Melbourne, Australia, Wednesday, Jan. 15, 2014.(AP Photo/Aaron Favila)
Novak Djokovic of Serbia waves to the crowd after winning his second round match against Leonardo Mayer of Argentina at the Australian Open tennis championship in Melbourne, Australia, Wednesday, Jan. 15, 2014.(AP Photo/Aaron Favila)