Japanese tennis player Kei Nishikori serves to US player Rajeev Ram (not shown) in their third round match at the Rogers Cup Men’s Singles Tennis tournament in Toronto, Canada, 28 July 2016. Nishikori defeated Ram 6-3, 6-4. EPA/WARREN TODA

Alexander Zverev of Germany returns a shot against Gael Monfils of France during their semifinals match of the Citi Open tennis tournament, at Rock Creek Park Tennis Center in Washington, DC, USA, 23 July 2016. EPA/ZACH GIBSON

Gael Monfils of France in against Ivo Karlovic of Croatia during the men’s final match of the Citi Open tennis tournament, at Rock Creek Park Tennis Center in Washington, DC, USA, 24 July 2016. EPA/ZACH GIBSON

Ivo Karlovic of Croatia in action against Gael Monfils of France during the men’s final match of the Citi Open tennis tournament, at Rock Creek Park Tennis Center in Washington, DC, USA, 24 July 2016. EPA/ZACH GIBSON

Japanese tennis player Kei Nishikori serves to US player Rajeev Ram (not shown) in their third round match at the Rogers Cup Men’s Singles Tennis tournament in Toronto, Canada, 28 July 2016. Nishikori defeated Ram 6-3, 6-4. EPA/WARREN TODA