Roger Federer of Switzerland falls as he plays against his compatriot Stan Wawrinka during their quarterfinal match for the French Open tennis tournament at Roland Garros in Paris, France, 02 June 2015. EPA/CAROLINE BLUMBERG

Ana Ivanovic of Serbia in action against Elina Svitolina of Ukraine during their quarterfinal match for the French Open tennis tournament at Roland Garros in Paris, France, 02 June 2015. EPA/ROBERT GHEMENT

Kei Nishikori of Japan in action against Jo-Wilfried Tsonga of France during their quarterfinal match for the French Open tennis tournament at Roland Garros in Paris, France, 02 June 2015. EPA/ROBERT GHEMENT

Novak Djokovic of Serbia in action against Richard Gasquet of France during their fourth round match for the French Open tennis tournament at Roland Garros in Paris, France, 01 June 2015. EPA/ROBERT GHEMENT

Stan Wawrinka of Switzerland in action against his compatriot Roger Federer during their quarterfinal match for the French Open tennis tournament at Roland Garros in Paris, France, 02 June 2015. EPA/IAN LANGSDON