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NEW YORK, NY - SEPTEMBER 06: Novak Djokovic of Serbia is congratulated by Roberto Bautista Agut of Spain after their Men's Singles Fourth Round match on Day Seven of the 2015 US Open at the USTA Billie Jean King National Tennis Center on September 6, 2015 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Matthew Stockman/Getty Images)

NEW YORK, NY - SEPTEMBER 06:  Novak Djokovic of Serbia is congratulated by Roberto Bautista Agut of Spain after their Men's Singles Fourth Round match on Day Seven of the 2015 US Open at the USTA Billie Jean King National Tennis Center on September 6, 2015 in the Flushing neighborhood of the Queens borough of New York City.  (Photo by Matthew Stockman/Getty Images)