Roger Federer of Switzerland celebrates defeating Kei Nishikori of Japan in their tennis match at the ATP World Tour finals at the O2 Arena in London November 11, 2014. REUTERS/Toby Melville
Roger Federer of Switzerland celebrates defeating Kei Nishikori of Japan in their tennis match at the ATP World Tour finals at the O2 Arena in London November 11, 2014. REUTERS/Toby Melville