NEW YORK, NY - SEPTEMBER 08: Novak Djokovic of Serbia returns a shot during his men's singles semifinal match against David Ferrer of Spain on Day Thirteen of the 2012 US Open at USTA Billie Jean King National Tennis Center on September 8, 2012 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Clive Brunskill/Getty Images)