Argentina's Juan Martin del Potro wrecked Rafael Nadal's US Open title aspirations with a bludgeoning 6-2, 6-2, 6-2 victory in the semifinals on Sunday.

The giant sixth seed was simply too powerful for the Spanish third seed, who was powerless to match the big-hitting coming at him from the other side of the net as his bid to win the US Open for the first time bit the dust.

Del Potro, who turns 21 next week, will play either title-holder and top seed Roger Federer of Switzerland or fourth seeded Novak Djokovic of Serbia in Monday's final.

"This is the best moment of my life," he said.

"I was so focussed every moment because Rafa is a great player and can run for five or six hours.

"I am not that strong, but I did my best and I am in the final."

Nadal, who endured his worst defeat in a Grand Slam tournament, said that he had been playing well early in the year before running into injury problems with his knees and then a stomach muscle strain.

"I had problems with serve and then to deal with a player like this, playing unbelievable tennis," he said.

Nadal, in only his second US Open semi-final, was out to become just the seventh player to complete a career Grand Slam of the four major titles having already won the French Open four times and Wimbledon and the Australian Open once each.

The 23-year-old from the Mediterranan island of Mallorca was in line to follow Fred Perry, Don Budge, Rod Laver, Roy Emerson, Andre Agassi and Federer, who completed the set at the French Open in June.

Del Potro, who turns 21 on September 23, was aiming to become the first South American US Open finalist since Guillermo Vilas won the title in 1977.

Both players had early break chances in a tightly-contested start to a match delayed by 24 hours because of heavy rain on Friday and Saturday.

But it was outsider Del Potro who struck first in the fourth game, unleashing a big forehand to get to break point and then forcing Nadal into hitting long on a backhand volley at the net.

There were no early signs of discomfort from Nadal from the stomach muscle strain that hampered him in earlier rounds, but he was simply being outhit by the giant South American who held easily to take a 4-1 lead.

Del Potro went into the match as the only player to defeat Nadal twice during the year, winning their last two matches in Miami and Montreal, both on hardcourts.

He continued that recent domination by breaking Nadal for a second time to take the first set, doing most of the damage with his big forehand, hit flat to either flank.

Nadal's problems worsened at the start of the second set as he started to look in some pain again from the abdominal injury and he promptly dropped serve again with a double fault on break point as Del Potro took a 3-1 lead.

The Argentinian staved off a fifth straight break point in the following game to lead 4-1 as Nadal looked anxiously towards coach Uncle Toni in the players' box.

Nadal was unable to stay the pace with the bigger man and he looked lost for answers as Del Potro broke once again to take the second set.

Del Potro held serve to open the third set and he pounced again in the following game, blasting Nadal's serves back with ease to break for the fifth time in the match.

The Argentinian eased to a 5-2 lead and then broke the Nadal serve to love to roar into the championship match.