Juan Martin del Potro reached his first grand slam final as he knocked out third seed Rafael Nadal in their US Open semi-final.

The sixth seed from Argentina blew Spain's Nadal away at Arthur Ashe Stadium, taking two hours and 20 minutes to win 6-2 6-2 6-2.

Del Potro will now face the winner of Sunday night's second semi-final between five-time defending champion Roger Federer and fourth seed Novak Djokovic.

"It's very difficult for me to speak at this moment," Del Potro said immediately following the victory. "I'm very, very happy, this is my favourite tournament and I can't believe this moment.

"I'm very close now to my dream to win this tournament. I hope to do it but I'm so happy to be here in this moment.

"If I win or lose tomorrow, I think this is the best moment of my life."

Nadal had run out of steam by the time he got to the US Open semi-finals 12 months ago, losing to Andy Murray in match stretched out over two days due to heavy rain and it appeared to be the case again as he was swept aside by Del Potro, just a month into his comeback from a bout of tendinitis in both knees following the French Open.

He had been unable to defend his title at Wimbledon and in his third tournament since returning following almost nine weeks out, he found no answer to an all-round display of tennis from the 6ft 6ins 20-year-old, also hampered by a stomach muscle issue that flared last month and was aggravated earlier this week.

Del Potro outpowered the left-hander on both serve and return and with forehand and backhand to deny Nadal a crack at completing a career Grand Slam.

Nadal, the Australian Open champion, pointed to his fitness problems but also credited Del Potro's performance.

"Halfway through the season having the problems with the knees and after that it's been difficult," Nadal said.

"But I'm very happy with the way I've come back, reaching the quarter-finals (in Montreal), semi-finals (in Cincinnati) and semi-finals (US Open).

"Here and in Cincinnati it was important for me because I had the right abdominal (injury) and that was a problem for me with the serve.

"But (Del Potro) has served very well and he's played unbelievable."

Del Potro had drawn first blood in with a break of serve in the fourth game to go 3-1 up and continued to pepper his rival with shots on the way to completing an excellent first set.

Nadal could not find an answer to the variety of powerful shots coming at him from all directions and he was soon a break point down in the second set, surrendering a 3-1 lead with a double fault.

Nadal saved four break points to win his second service game of the set but at 4-2 down he was looking at a mountain to climb.

Del Potro was like a boxer as he took apart Nadal with a deluge of punches, earning triple set point at 5-2 with a powerful combination of forehand and then backhand winner, the second seed stranded at the back of the court.

Nadal had taken just four games in the first two sets but had not been without his opportunities, earning five break points but converting none.

He was soon behind in the third set as Del Potro was looking unstoppable, moving to 3-0 up with another booming forehand to win the game to love.

Nadal finally got on the board with holds of serve in the fourth and sixth game but Del Potro was still in the ascendancy, seemingly sending down winners at will as his deflated rival watched them sail by.

Nadal served to stay in the match at 5-2 down but despite his fighting spirit, Del Potro was too strong.

The Spaniard netted a forehand and was then passed as the Argentine earned triple match point.

A huge forehand had Nadal at full stretch to return off his own forehand but again he was being sent from end to end of the baseline and the match was over when a last, desperate forehand was sent long.