Roger Federer of Switzerland reacts during his semi-final tennis match against compatriot Stanislas Wawrinka at the ATP World Tour Finals at the O2 Arena in London November 15, 2014. REUTERS/Toby Melville
Roger Federer of Switzerland reacts during his semi-final tennis match against compatriot Stanislas Wawrinka at the ATP World Tour Finals at the O2 Arena in London November 15, 2014. REUTERS/Toby Melville