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NEW YORK, NEW YORK - AUGUST 30: Novak Djokovic of Serbia returns a shot during his third round Men's Singles match against Denis Kudla of the United States on day five of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 30, 2019 in Queens borough of New York City. (Photo by Chaz Niell/Getty Images)

NEW YORK, NEW YORK - AUGUST 30:  Novak Djokovic of Serbia returns a shot during his third round Men's Singles match against Denis Kudla of the United States on day five of the 2019 US Open at the USTA Billie Jean King National Tennis Center on August 30, 2019 in Queens borough of New York City. (Photo by Chaz Niell/Getty Images)