NEW YORK, NY - AUGUST 29: Novak Djokovic of Serbia in action during his first round match on day 1 of the 2016 US Open at USTA Billie Jean King National Tennis Center on August 29, 2016 in New York City. (Photo by Jean Catuffe/Getty Images)

NEW YORK, NY - AUGUST 29: Novak Djokovic of Serbia in action during his first round match on day 1 of the 2016 US Open at USTA Billie Jean King National Tennis Center on August 29, 2016 in New York City. (Photo by Jean Catuffe/Getty Images)