Djokovic of Serbia serves to Wawrinka of Switzerland during their men's semi-final match at the U.S....
Novak Djokovic of Serbia serves to Stanislas Wawrinka of Switzerland during their men's semi-final match at the U.S. Open tennis championships in New York September 7, 2013. REUTERS/Kena Betancur (UNITED STATES - Tags: SPORT TENNIS)