The Argentine won that decider by 7-4 to set up the first Open five-set final since Andre Agassi topped fellow-American Todd Martin 10 years ago.

Taking advantage of Federer's faulty serve, Del Potro broke the French Open and Wimbledon champion in the second game of the fifth set and cemented his advantage by breaking the Swiss master again in the final game.

"I got off to a good start and had many more chances to make a difference," Federer told reporters. "He hung in there and gave himself chances, and in the end he was a better man."

Del Potro had 37 winners off his huge forehand and took advantage of a poor serving performance by Federer, who successfully landed only half of his first serves and double-faulted 11 times.

Federer, whose last defeat at Flushing Meadows came against Argentine David Nalbandian in the fourth round of the 2003 tournament, fell short of matching American Bill Tilden's mark of six US titles in a row in the 1920s.

"You can't have them all," he said.

"I've had an amazing summer and a great run."