Stanislas Wawrinka of Switzerland serves the ball to Juan Monaco of Argentina during their second round match of the Italian Open tennis tournament at the Foro Italico in Rome, Italy, 12 May 2015. EPA/ETTORE FERRARI

Novak Djokovic of Serbia returns the ball to Nicolas Almagro of Spain during their match for the Italian Open tennis tournament at the Foro Italico in Rome, Italy, 12 May 2015. EPA/CLAUDIO ONORATI

Sabine Lisicki of Germany returns the ball to Timea Bacsinszky of Switzerland during their second round match of the Italian Open tennis tournament at the Foro Italico in Rome, Italy, 12 May 2015. EPA/CLAUDIO ONORATI

Serena Williams of the USA returns the ball to Anastasia Pavlyuchenkova of Russia during their second round match for the Italian Open tennis tournament at the Foro Italico in Rome, Italy, 12 May 2015. EPA/ETTORE FERRARI

Elina Svitolina of Ukraine returns the ball to Flavia Pennetta of Italy during their first round match of the Italian Open tennis tournament at the Foro Italico in Rome, Italy, 12 May 2015. EPA/CLAUDIO ONORATI