Novak Djokovic of Serbia plays a return to Jo-Wilfried Tsonga of France during their singles tennis match at the ATP World Tour Finals in London Monday, Nov. 5, 2012. (AP Photo/Kirsty W

 

              Novak Djokovic of Serbia plays a return to Jo-Wilfried Tsonga of France during their singles tennis match at the ATP World Tour Finals in London Monday, Nov. 5, 2012. (AP Photo/Kirsty W
Novak Djokovic of Serbia plays a return to Jo-Wilfried Tsonga of France during their singles tennis match at the ATP World Tour Finals in London Monday, Nov. 5, 2012. (AP Photo/Kirsty Wigglesworth)