NEW YORK, NY - SEPTEMBER 01:  Frances Tiafoe of the United States returns a shot to Viktor Troicki of Serbia during their Men's Singles First Round match on Day Two of the 2015 US Open at the USTA Billie Jean King National Tennis Center on September 1, 2015 in the Flushing neighborhood of the Queens borough of New York City.  (Photo by Clive Brunskill/Getty Images)