Switzerland’s Roger Federer returns to Britain’s Andy Murray during a round robin match at the ATP World Tour Finals mens tennis tournament at the O2 Arena in London, Britain, 13 November 2014. EPA/ANDY RAIN

Britain’s Andy Murray returns to Switzerland’s Roger Federer during a round robin match at the ATP World Tour Finals mens tennis tournament at the O2 Arena in London, Britain, 13 November 2014. EPA/ANDY RAIN

Switzerland’s Roger Federer serves to Britain’s Andy Murray during a round robin match at the ATP World Tour Finals mens tennis tournament at the O2 Arena in London, Britain, 13 November 2014. EPA/ANDY RAIN

Britain’s Andy Murray during his 6-0 6-1 loss to Switzerland’s Roger Federer in their round robin match at the ATP World Tour Finals mens tennis tournament at the O2 Arena in London, Britain, 13 November 2014. EPA/ANDY RAIN

Switzerland’s Roger Federer reacts following his victory over Britain’s Andy Murray during a round robin match at the ATP World Tour Finals mens tennis tournament at the O2 Arena in London, Britain, 13 November 2014 . EPA/ANDY RAIN

Britain’s Andy Murray returns to Switzerland’s Roger Federer during a round robin match at the ATP World Tour Finals mens tennis tournament at the O2 Arena in London, Britain, 13 November 2014. EPA/ANDY RAIN

Britain’s Andy Murray (L) following his 6-0 6-1 defeat by Switzerland’s Roger Federer (R) during a round robin match at the ATP World Tour Finals mens tennis tournament at the O2 Arena in London, Britain, 13 November 2014 . EPA/ANDY RAIN