Rafael Nadal of Spain in action against Jack Sock of the USA during their quarterfinal match in the China Open tennis tournament at the National Tennis Center in Beijing, China, 09 October 2015. EPA/HOW HWEE YOUNG

Kei Nishikori of Japan hits a return to Marin Cilic of Croatia during the men’s singles quarterfinal match of the Japan Open Tennis Championships in Tokyo, Japan, 09 October 2015. EPA/KIYOSHI OTA

Fans reach for a wristband thrown by Novak Djokovich of Serbia after his quarterfinal match against John Isner of USA in the China Open tennis tournament at the National Tennis Center in Beijing, China, 09 October 2015. EPA/HOW HWEE YOUNG

Ana Ivanovic of Serbia in action against Anastasia Pavlyuchenkova of Russia during their quarter final match for the China Open tennis tournament at the National Tennis Center in Beijing, China, 09 October 2015. EPA/HOW HWEE YOUNG

Stan Wawrinka of Switzerland hits a return to Austin Krajicek of the USA during the men’s singles quarterfinal match of the Japan Open Tennis Championships in Tokyo, Japan, 09 October 2015. EPA/KIYOSHI OTA