NEW YORK, NY - SEPTEMBER 09:  Kei Nishikori of Japan reacts against Stan Wawrinka of Switzerland during their Men's Singles Semifinal Match on Day Twelve of the 2016 US Open at the USTA Billie Jean King National Tennis Center on September 9, 2016 in the Flushing neighborhood of the Queens borough of New York City.  (Photo by Al Bello/Getty Images)