Roger Federer of Switzerland reacts to a game win against Janko Tipsarevic of Serbia, during their ATP World Tour Finals singles tennis match at the O2 Arena in London, Tuesday, Nov. 6, 2012. (AP Photo/Sang Tan)

Associated Press
Roger Federer of Switzerland reacts to a game win against Janko Tipsarevic of Serbia, during their ATP World Tour Finals singles tennis match at the O2 Arena in London, Tuesday, Nov. 6, 2012. (AP Photo/Sang Tan)
Roger Federer of Switzerland reacts to a game win against Janko Tipsarevic of Serbia, during their ATP World Tour Finals singles tennis match at the O2 Arena in London, Tuesday, Nov. 6, 2012. (AP Photo/Sang Tan)
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