CINCINNATI, OH - AUGUST 23: Novak Djokovic of Serbia returns a forehand to Roger Federer of Switzerland during the final round on Day 9 of the Western & Southern Open at the Lindner Family Tennis Center on August 23, 2015 in Cincinnati, Ohio. (Photo by Maddie Meyer/Getty Images)
CINCINNATI, OH - AUGUST 23: Novak Djokovic of Serbia reacts during his final round match against Roger Federer of Switzerland on Day 9 of the Western & Southern Open at the Lindner Family Tennis Center on August 23, 2015 in Cincinnati, Ohio. (Photo by Maddie Meyer/Getty Images)
CINCINNATI, OH - AUGUST 21: Novak Djokovic of Serbia returns a forehand to Stanislas Wawrinka of Switzerland during Day 7 of the Western & Southern Open at the Lindner Family Tennis Center on August 21, 2015 in Cincinnati, Ohio. (Photo by Maddie Meyer/Getty Images)
