Flushing Meadows, NY -- (Sports Network) - Rafael Nadal fell behind early in his late-night match Wednesday, but then dominated American Mardy Fish to reach his first semifinal at the U.S. Open.

The top-ranked Spaniard won 3-6, 6-1, 6-4, 6-2 with the match ending after 2 a.m.

"This court was always very difficult for me, but I'm very happy," said Nadal, who was put to the test early, but pulled through in his quest for a third Grand Slam title this year after triumphs at the French Open and Wimbledon.

In fact, Nadal has now reached the semifinals at all four Grand Slams this year.

Ahead for Nadal will be another man in unchartered waters - sixth seed Andy Murray of Great Britain. He reached the semifinals 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.

Fish, who had 14 aces to just three for Nadal, broke serve at the start of the match and carried that lead throughout the first set. The tide turned in the second though, and in the third Nadal broke to go up 4-3. Fish, who hit a forehand into the net to end the set, was his own worst enemy. He committed 53 unforced errors to just 19 for Nadal.

Nadal broke serve to go up 2-1 in the fourth set, moving Fish to smash his racket in frustration during the changeover. Fish had several long returns in that final set, finally ending the match with another one over the end line.

Still, Nadal gave compliments to Fish for his effort.

"Mardy played unbelievable in the first set, aggressive," said Nadal. "He was serving very well."

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.

"Like I said in all my other matches, I don't care what happens throughout the course of the match as long as I win," said Murray. "I played the big points great. In the first two sets I played really well in the tiebreaks."

Nadal has the upperhand going into the semifinals with a 5-0 match record against Murray. That includes three wins this year, all in straight sets, including a quarterfinal match at Wimbledon.

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.