Serbia's Novak Djokovic, left, jokes with a member of his training staff during a training session at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 13, 2013. (AP Photo/Dita Alangkara)

Associated Press
Serbia's Novak Djokovic, left, jokes with a member of his training staff during a training session at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 13, 2013. (AP Photo/Dita Alangkara)
Serbia's Novak Djokovic, left, jokes with a member of his training staff during a training session at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 13, 2013. (AP Photo/Dita Alangkara)
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