Rafael Nadal had to dig deep to reach the semi-finals of the US Open after losing the first set to Mardy Fish.

The world No 1 eventually found his game to secure victory 3-6, 6-1, 6-4, 6-2 and will now face Andy Murray, who defeated Juan Martín Del Potro late last night.

Nadal, who is the reigning Wimbledon, French Open and Olympic champion, has never been this far at the US Open. Only Rod Laver, Pete Sampras and Roger Federer have won three grand slam titles in a row in the 40-year Open era. He holds a has a 5-0 record against Murray.

Saturday's other semi-final pairing will be decided later today when four-time defending champion Federer meets Luxembourg qualifier Gilles Muller and Serbian third seed Novak Djokovic faces US eighth seed Andy Roddick.

"I'm very happy for being the first time in the semi-finals of the US Open," Nadal said. "Mardy played very well in the first set, served unbelievably well.

"It's going to be very difficult [against Murray]. I'm going to have to play my best. He's coming with big confidence. He's doing very well. I expect a very tough match."

Nadal, 22, has won an ATP-best 41 hardcourt matches this year and seeks his ninth title of the season. He has won 54 of his past 56 matches, losing only to Juan Carlos Ferrero at Rome and Djokovic at Cincinnati.

Murray pushed Nadal to five sets in their first meeting, in the fourth round of last year's Australian Open, but has not taken a set off him since.

Nadal improved to 5-0 against Fish, who had not taken a set off the Spaniard until the clock struck midnight at Arthur Ashe Stadium.

Fish, who had never been past the second round of the US Open in eight prior appearances, took advantage of his only break-point chance of the first set and denied Nadal on three break opportunities to claim the first set in 39 minutes, firing 23 winners and winning 16 of 18 first-serve points.

Nadal responded by breaking Fish in the second game of the second set, broke again to 5-1 when Fish netted a forehand and held to level the match. Fish netted a forehand volley to offer up the first break points of the third set. He saved the first with an ace but Nadal struck with a forehand winner for the break and a 4-3 edge and held serve to claim the set.

Nadal broke at love in the third game of the fourth set when Fish pushed a backhand wide. Moments later, the American spat on his racquet and smashed it on the ground during a changeover break.