gettyimagesNEW YORK, NY - SEPTEMBER 03: Kei Nishikori of Japan returns a shot against Stan Wawrinka of Switzerland during their men's singles quarterfinal match on Day Ten of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 3, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Matthew Stockman/Getty Images)