Coco Vandeweghe of the US hits a return to Garbine Muguruza of Spain during their second round match of the Western & Southern Open tennis championships at the Linder Family Tennis Center in Mason, near Cincinnati, Ohio, USA, 17 August 2016. EPA/TANNEN MAURY

Garbine Muguruza of Spain hits a return shot to Coco Vandeweghe of the US during their second round match of the Western & Southern Open tennis championships at the Linder Family Tennis Center in Mason, near Cincinnati, Ohio, USA, 17 August 2016. EPA/TANNEN MAURY

Kristine Mladenovic of France hits a return shot to Angelique Kerber of Germany during their second round match of the Western & Southern Open tennis championships at the Linder Family Tennis Center in Mason, near Cincinnati, Ohio, USA, 17 August 2016. EPA/TANNEN MAURY

Lucie Safarova of the Czech Republic serves to Andrea Petkovic of Germany in their first round match of the Western & Southern Open tennis championships at the Linder Family Tennis Center in Mason, near Cincinnati, Ohio, USA, 17 August 2016. EPA/TANNEN MAURY

Viktorija Golubic of Switzerland hits a return shot to Kurumi Nara of Japan in their first round match of the Western & Southern Open tennis championships at the Linder Family Tennis Center in Mason, near Cincinnati, Ohio, USA, 17 August 2016. EPA/TANNEN MAURY