NEW YORK, NY - SEPTEMBER 05:  Serena Williams in action against Madison Keys of the United States (not seen) of the United States during their Women's Singles Fourth Round match on Day Seven of the 2015 US Open at the USTA Billie Jean King National Tennis Center in New York City, on September 6, 2015. (Photo by Cem Ozdel/Anadolu Agency/Getty Images)