gettyimagesNEW YORK, NY - SEPTEMBER 06: Kei Nishikori of Japan celebrates after defeating Novak Djokovic of Serbia in their men's singles semifinal match on Day Thirteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 6, 2014 in the Flushing neighborhood of the Queens borough of New York City. Nishikori defeated Djokovic in four sets 6-4, 1-6, 7-6, 6-3. (Photo by Julian Finney/Getty Images)