Serena Williams of the USA in action against Maria Sharapova of Russia during their semi final match for the Wimbledon Championships at the All England Lawn Tennis Club, in London, Britain, 09 July 2015. EPA/SEAN DEMPSEY

Serena Williams of the USA in action against Maria Sharapova of Russia during their semi final match for the Wimbledon Championships at the All England Lawn Tennis Club, in London, Britain, 09 July 2015. EPA/SEAN DEMPSEY

Serena Williams of the US returns to Maria Sharapova of Russia in their semi final match during the Wimbledon Championships at the All England Lawn Tennis Club, in London, Britain, 09 July 2015. EPA/FACUNDO ARRIZABALAGA

Serena Williams of the USA in action against Victoria Azarenka of Belarus during their quarter final match for the Wimbledon Championships at the All England Lawn Tennis Club, in London, Britain, 07 July 2015. EPA/FACUNDO ARRIZABALAGA

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