Flushing Meadows, NY -- (Sports Network) - Sixth seed Andy Murray of Great Britain reached the semifinals at the U.S. Open on Wednesday with a tough four-set victory over 17th seed Juan Martin del Potro of Argentina.

Murray secured his first-ever spot in a Grand Slam semifinal with a 7-6 (7-2), 7-6 (7-1), 4-6, 7-5 victory in a match that took nearly four hours to complete on Day 10 at the USTA Billie Jean King National Tennis Center.

Murray fired nine aces and overcame 61 unforced errors, but came through when it counted to stop a 23-match winning streak for the 19-year-old del Potro. That included titles in his last four events.

Murray held serve to go ahead 6-5 and then won the first two points of the 12th game of the final set. Del Potro fired a forehand winner, but then returned a ball into the net.

Del Potro saved one match point, but a wide return sent Murray into the semis against the winner of tonight's late match between top-ranked Rafael Nadal and American Mardy Fish.

The other quarterfinal matches will be played here on Thursday, with second- seeded, former No. 1 and reigning four-time U.S. Open champion Roger Federer taking on upstart Gilles Muller of Luxembourg and third-seeded Novak Djokovic battling eighth-seeded American Andy Roddick. Djokovic is the reigning Aussie Open champ and was last year's U.S. Open runner-up to the 12-time major titlist Federer, while Roddick is a former world No. 1 who titled here back in 2003.