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MELBOURNE, AUSTRALIA - JANUARY 22: Novak Djokovic of Serbia serves in his second round match against Andrey Kuznetsov of Russia during day four of the 2015 Australian Open at Melbourne Park on January 22, 2015 in Melbourne, Australia. (Photo by Scott Barbour/Getty Images)

MELBOURNE, AUSTRALIA - JANUARY 22:  Novak Djokovic of Serbia serves in his second round match against Andrey Kuznetsov of Russia during day four of the 2015 Australian Open at Melbourne Park on January 22, 2015 in Melbourne, Australia.  (Photo by Scott Barbour/Getty Images)