Russian tennis player Maria Sharapova during the Madrid Open tennis tournament semi-finals match played against her countrywoman Svetlana Kuznetsova at Caja Magica Pavilion, in Madrid, Spain, 08 May 2015. EPA/Chema Moya

Spanish tennis player Rafa Nadal returns the ball to Bulgarian Grigor Dimitrov during their Madrid Open tennis tournament quarter final match played at Caja Magica pavilion, in Madrid, Spain, 08 May 2015. EPA/JuanJo Martin

Czech tennis player Petra Kvitova during the Madrid Open tennis tournament semi-finals match played against US Serena Williams at Caja Magica Pavilion, in Madrid, Spain, 08 May 2015. EPA/Chema Moya

Canadian tennis player Milos Raonic in action against British Andy Murray during their quarterfinal match for the Madrid Open tennis tournament at Caja Magica pavilion, in Madrid, Spain, 08 May 2015. EPA/Alberto Martin

Spanish tennis player David Ferrer in action against Japanese Kei Nishikori during their quarterfinal match for the Madrid Open tennis tournament at Caja Magica pavilion, in Madrid, Spain, 08 May 2015. EPA/Alberto Martin

Japanese tennis player Kei Nishikori in action against Spanish David Ferrer during their quarterfinal match for the Madrid Open tennis tournament at Caja Magica pavilion, in Madrid, Spain, 08 May 2015. EPA/Alberto Martin