
Novak Djokovic of Serbia hits a return during the men's singles quarter-final match against Feliciano Lopez of Spain at the 2015 US Open in New York, the United States, on Sept. 8, 2015. Novak Djokovic won 3-1. (Xinhua/Qin Lang)

Novak Djokovic of Serbia hits a return during the men's singles quarter-final match against Feliciano Lopez of Spain at the 2015 US Open in New York, the United States, on Sept. 8, 2015. Novak Djokovic won 3-1. (Xinhua/Qin Lang)