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NEW YORK, NY - AUGUST 29: Polona Hercog of Slovenia serves to Angelique Kerber of Germany during her first round Women's Singles match on Day One of the 2016 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2016 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Elsa/Getty Images)

NEW YORK, NY - AUGUST 29:  Polona Hercog of Slovenia serves to Angelique Kerber of Germany during her first round Women's Singles match on Day One of the 2016 US Open at the USTA Billie Jean King National Tennis Center on August 29, 2016 in the Flushing neighborhood of the Queens borough of New York City.  (Photo by Elsa/Getty Images)