Juan Martin Del Potro of Argentina plays a return to Roger Federer of Switzerland, during their singles tennis match at the ATP World Tour Finals, in London, Saturday, Nov. 10, 2012. (AP Photo/Sang ... more 
Juan Martin Del Potro of Argentina plays a return to Roger Federer of Switzerland, during their singles tennis match at the ATP World Tour Finals, in London, Saturday, Nov. 10, 2012. (AP Photo/Sang Tan) less 
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Associated Press | Photo By Sang Tan
Sat, Nov 10, 2012 12:25 PM EST