MASON, OH - AUGUST 18: Novak Djokovic of Serbia hits a backhand against Juan Martin Del Potro of Argentina during day eight of the Western & Southern Open at Lindner Family Tennis Center on August 18, 2012 in Mason, Ohio. (Photo by Nick Laham/Getty Images)
MASON, OH - AUGUST 18: Novak Djokovic of Serbia hits a backhand against Juan Martin Del Potro of Argentina during day eight of the Western & Southern Open at Lindner Family Tennis Center on August 18, 2012 in Mason, Ohio. (Photo by Nick Laham/Getty Images)
