Viktoria Azarenka of Belarus returns to Kirsten Flipkens of Belgium in their second round match during the Wimbledon Championships at the All England Lawn Tennis Club, in London, Britain, 01 July 2015. EPA/GERRY PENNY

Stan Wawrinka of Switzerland returns to Victor Estrella Burgos of Dominican Republic in their second round match during the Wimbledon Championships at the All England Lawn Tennis Club, in London, Britain, 01 July 2015. EPA/SEAN DEMPSEY

Serena Williams of the USA in action against Timea Babos of Hungary during their second round match for the Wimbledon Championships at the All England Lawn Tennis Club, in London, Britain, 01 July 2015. EPA/ANDY RAIN

Kirsten Flipkens of Belgium returns to Viktoria Azarenka of Belarus in their second round match during the Wimbledon Championships at the All England Lawn Tennis Club, in London, Britain, 01 July 2015. EPA/GERRY PENNY

Maria Sharapova of Russia in action against Richel Hogenkamp of the Netherlands during their second round match for the Wimbledon Championships at the All England Lawn Tennis Club, in London, Britain, 01 July 2015. EPA/FACUNDO ARRIZABALAGA