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NEW YORK, NY - AUGUST 31: John Isner of the United States serves to Steve Darcis of Belgium during his second round Men's Singles match on Day Three of the 2016 US Open at the USTA Billie Jean King National Tennis Center on August 31, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Joe Scarnici/Getty Images)

NEW YORK, NY - AUGUST 31:  John Isner of the United States serves to Steve Darcis of Belgium during his second round Men's Singles match on Day Three of the 2016 US Open at the USTA Billie Jean King National Tennis Center on August 31, 2016 in the Flushing neighborhood of the Queens borough of New York City.  (Photo by Joe Scarnici/Getty Images)