Stan Wawrinka of Switzerland in action against Borna Coric of Croatia during their second round match at the Western & Southern Open at the Linder Family Tennis Center in Mason, near Cincinnati, Ohio, USA, 19 August 2015. EPA/TANNEN MAURY

The court is reflected in the sun glasses of Jerzy Janowicz of Poland as he faces Jared Donaldson of the US during their second round match at the Western & Southern Open at the Linder Family Tennis Center in Mason, near Cincinnati, Ohio, USA, 19 August 2015. EPA/TANNEN MAURY

Thanasi Kokkinakis of Australia in action against Richard Gasquet of France during their second round match at the Western & Southern Open at the Linder Family Tennis Center in Mason, near Cincinnati, Ohio, USA, 19 August 2015. EPA/TANNEN MAURY

Serena Williams of the US in action against Tsvetana Pironkova of Bulgaria during their second round match at the Western & Southern Open at the Linder Family Tennis Center in Mason, near Cincinnati, Ohio, USA, 19 August 2015. EPA/TANNEN MAURY

Simona Halep of Romania in action against Kristina Mladenovic of France during their second round match at the Western & Southern Open at the Linder Family Tennis Center in Mason, near Cincinnati, Ohio, USA, 19 August 2015. EPA/TANNEN MAURY

Borna Coric of Croatia in action against Stan Wawrinka of Switzerland during their second round match at the Western & Southern Open at the Linder Family Tennis Center in Mason, near Cincinnati, Ohio, USA, 19 August 2015. EPA/TANNEN MAURY