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NEW YORK, NEW YORK - SEPTEMBER 03: Roger Federer of Switzerland serves during his Men's Singles quarterfinal match against Grigor Dimitrov of Bulgaria on day nine of the 2019 US Open at the USTA Billie Jean King National Tennis Center on September 03, 2019 in the Queens borough of New York City. (Photo by Steven Ryan/Getty Images)

NEW YORK, NEW YORK - SEPTEMBER 03:  Roger Federer of Switzerland serves during his Men's Singles quarterfinal match against Grigor Dimitrov of Bulgaria on day nine of the 2019 US Open at the USTA Billie Jean King National Tennis Center on September 03, 2019 in the Queens borough of New York City. (Photo by Steven Ryan/Getty Images)