<p>Spain's David Ferrer returns a shot against Janko Tipsarevic of Serbia in the quarterfinals during the 2012 US Open tennis tournament, Thursday, Sept. 6, 2012, in New York. (AP Photo/Peter Morgan)</p>
September 7, 2012
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September 7, 2012 9:15 p.m.
Djokovic reaches another Slam semi
Ferrer needs 4 hours, 31 minutes to defeat Tipsarevic
NEW YORK (AP) - Locked in a taut, thrill-a-minute second set, Novak Djokovic and Juan Martin del Potro headed to a tiebreaker and promptly produced a 20-stroke masterpiece of a point befitting a pair of past U.S. Open champions.