Rafael Nadal from Spain in action against Fernando Verdasco from Spain during their third round match at the BNP Paribas Open tennis tournament in Indian Wells, California, USA, 15 March 2016. EPA/MIKE NELSON

John Isner of USA in action against Adrian Mannarino of France during their third round match at the BNP Paribas Open tennis tournament in Indian Wells, California, USA, 15 March 2016. Isner won the match 6-4,7-6(4). EPA/PAUL BUCK

Jelena Jankovic from Serbia serves against Agnieszka Radwanska from Poland during their fourth round match at the BNP Paribas Open tennis tournament in Indian Wells, California, USA, 15 March 2016. EPA/MIKE NELSON

Steve Johnson of the USA in action against Kei Nishikori from Japan during their third round match at the BNP Paribas Open tennis tournament in Indian Wells, California, USA, 15 March 2016. EPA/MIKE NELSON

Alexander Zverev of Germany in action against Gilles Simon of France during their third round match at the BNP Paribas Open in Indian Wells, California, USA, 15 March 2016. EPA/JOHN G. MABANGLO