
Novak Djokovic of Serbia hits a return to John Isner of the United States during their men's singles quarterfinal at the China Open tennis tournament in Beijing, China, Oct. 9, 2015. Djokovic won 2-0. (Xinhua/Xing Guangli)

Novak Djokovic of Serbia hits a return to John Isner of the United States during their men's singles quarterfinal at the China Open tennis tournament in Beijing, China, Oct. 9, 2015. Djokovic won 2-0. (Xinhua/Xing Guangli)