Thanasi Kokkinakis of Australia in action against Bernard Tomic of Australia during their second round match for the French Open tennis tournament at Roland Garros in Paris, France, 28 May 2015. EPA/CAROLINE BLUMBERG

Petra Kvitova of Czech Republic in action against Silvia Soler-Espinosa of Spain during their second round match for the French Open tennis tournament at Roland Garros in Paris, France, 28 May 2015. EPA/ROBERT GHEMENT

Rafael Nadal of Spain in action against Nicolas Almagro of Spain during their second round match for the French Open tennis tournament at Roland Garros in Paris, France, 28 May 2015. EPA/IAN LANGSDON

Andy Murray of Britain reacts as he plays against Joao Sousa of Portugal during their second round match for the French Open tennis tournament at Roland Garros in Paris, France, 28 May 2015. EPA/IAN LANGSDON

Serena Williams of the USA in action against Anna-Lena Friedsam of Germany during their second round match for the French Open tennis tournament at Roland Garros in Paris, France, 28 May 2015. EPA/ROBERT GHEMENT