Dominic Thiem from Austria in action against Jo-Wilfried Tsonga from France during their fourth round match at the BNP Paribas Open tennis tournament in Indian Wells, California, USA, 16 March 2016. EPA/MIKE NELSON

Simona Halep from Romania in action against Serena Williams of the USA during their quarterfinal match at the BNP Paribas Open tennis tournament in Indian Wells, California, USA, 16 March 2016. EPA/MIKE NELSON

John Isner of USA in action against Kei Nishikori of Japan during their fourth round match at the BNP Paribas Open tennis tournament in Indian Wells, California, USA, 16 March 2016. EPA/PAUL BUCK

Agnieszka Radwanska from Poland in action against Petra Kvitova from the Czech Republic during their quarterfinals match at the BNP Paribas Open tennis tournament in Indian Wells, California, USA, 16 March 2016. EPA/MIKE NELSON

Richard Gasquet from France in action against Marin Cilic from Croatia during their fourth round match at the BNP Paribas Open tennis tournament in Indian Wells, California, USA, 16 March 2016. EPA/MIKE NELSON