Roger Federer of Switzerland hits a return to Andy Murray of Great Britain in their quarter-finals match of the Western & Southern Open tennis tournament at the Linder Tennis Center in Mason, Ohio, USA, 15 August 2014. EPA/TANNEN MAURY

Roger Federer of Switzerland hits a return shot to Gael Monfils of France in their third round match of the Western & Southern Open tennis tournament at the Linder Tennis Center in Mason, Ohio, USA, 14 August 2014. EPA/TANNEN MAURY

Roger Federer of Switzerland hits a return shot to Gael Monfils of France in their third round match of the Western & Southern Open tennis tournament at the Linder Tennis Center in Mason, Ohio, USA, 14 August 2014. EPA/TANNEN MAURY

Roger Federer of Switzerland serves to Gael Monfils of France in their third round match of the Western & Southern Open tennis tournament at the Linder Tennis Center in Mason, Ohio, USA, 14 August 2014. EPA/TANNEN MAURY

Roger Federer of Switzerland hits a return shot to Vasek Pospisil of Canada in their second round match of the Western & Southern Open tennis tournament at the Linder Tennis Center in Mason, Ohio, USA, 13 August 2014. EPA/TANNEN MAURY

Roger Federer of Switzerland hits a backhand return to Vasek Pospisil of Canada in their second round match of the Western & Southern Open tennis tournament at the Linder Tennis Center in Mason, Ohio, USA, 13 August 2014. EPA/TANNEN MAURY