Kei Nishikori of Japan serves to Andy Murray of Great Britain during their quarterfinals round match on the tenth day of the US Open Tennis Championships at the USTA National Tennis Center in Flushing Meadows, New York, USA, 07 September 2016. The US Open runs through September 11. EPA/ANDREW GOMBERT

Andy Murray of Great Britain hits a return to Kei Nishikori of Japan during their quarterfinals round match on the tenth day of the US Open Tennis Championships at the USTA National Tennis Center in Flushing Meadows, New York, USA, 07 September 2016. The US Open runs through September 11. EPA/ANDREW GOMBERT

Kei Nishikori of Japan (R) hits a return to Andy Murray of Great Britain during their quarterfinals round match on the tenth day of the US Open Tennis Championships at the USTA National Tennis Center in Flushing Meadows, New York, USA, 07 September 2016. The US Open runs through September 11. EPA/JUSTIN LANE

Andy Murray of Great Britain chases but cannot hit a return to Kei Nishikori of Japan during their quarterfinals round match on the tenth day of the US Open Tennis Championships at the USTA National Tennis Center in Flushing Meadows, New York, USA, 07 September 2016. The US Open runs through September 11. EPA/JUSTIN LANE

Andy Murray of Great Britain reacts as he plays Kei Nishikori of Japan during their quarterfinals round match on the tenth day of the US Open Tennis Championships at the USTA National Tennis Center in Flushing Meadows, New York, USA, 07 September 2016. The US Open runs through September 11. EPA/JUSTIN LANE

Kei Nishikori of Japan (L) and Andy Murray of Great Britain at the net after their quarterfinals round match on the tenth day of the US Open Tennis Championships at the USTA National Tennis Center in Flushing Meadows, New York, USA, 07 September 2016. The US Open runs through September 11. EPA/ANDREW GOMBERT