NEW YORK, NY - SEPTEMBER 6 : Novak Djokovic of Serbia returns the ball to Kei Nishikori of Japan during their men's singles semifinal match on Day 13 of the 2014 US Open at the USTA Billie Jean King National Tennis Center in New York, United States on September 6, 2014. (Photo by Bilgin Sasmaz/Anadolu Agency/Getty Images)
