Novak Djokovic of Serbia celebrates after defeating Lukas Lacko of Slovakia in their first round match at the Australian Open tennis championship in Melbourne, Australia, Monday, Jan. 13, 2014..(AP Photo/Aaron Favila)
Novak Djokovic of Serbia makes a forehand return to Lukas Lacko of Slovakia during their first round match at the Australian Open tennis championship in Melbourne, Australia, Monday, Jan. 13, 2014.(AP Photo/Eugene Hoshiko)