By Olayinka Abiola

It was the first time since 2003, when Del Potro was just 14 years old, that Federer had lost a match on the cement courts at Flushing Meadows.

Del Potro is the first man other than Rafael Nadal to beat Federer in the final of a Grand Slam tournament.

Swiss star Federer, 28, had been going for a record-equalling sixth consecutive title at Flushing Meadows set by American Bill Tilden in 1925.

It was the first time since Andre Agassi beat Todd Martin 10 years ago that the US Open final had gone to a decider, and the experience and fitness of Federer suggested he would start favourite.

Federer went into the match on a 40-match unbeaten run in New York, his last defeat coming against another Argentine, David Nalbandian, in the fourth round in 2003.

He also held a 6-0-career record against Del Potro and was playing in his 22nd Grand Slam final, targeting a 16th major win.

However, Del Potro has rocketed up the rankings over the last year and pushed Federer desperately close over five sets in the French Open semi-finals in June. His 6-2 6-2 6-2 demolition of Nadal in the semi-finals also left no one in any doubt that he posed a real threat to Federer.

Federer took a 3-0 lead in 15 minutes, winning one point by racing about 5 feet wide of the doubles alley for a defensive backhand, then sprinting the other way for a cross-court forehand passing winner that he celebrated by yelling and shaking his fists.

At 5-4 in the second set, Federer served for a two-set lead, and at 30-0 everything seemed to be going his way. At 30-30, Del Potro struck an outrageous forehand down the line. The linejudge called the ball out, giving Federer a 40-30 lead in the game and a set point. But Del Potro challenged the call with the Hawk-Eye technology, and the replay on the video screen indicated that the ball had, indeed, hit the outside of the line. So Federer’s set point was taken away from him. Federer was not convinced that the computer got this one right, and he went back to inspect the 'mark’ on the side of the line. Whatever Federer’s complaints, he was 30-40 down, and Del Potro took his breakpoint with another forehand winner down the line. There was no argument about that one. Suddenly Del Potro was a different player, suddenly he was swinging at his forehands.

Del Potro’s forehand was hugely effective in the tiebreak; that was the shot that the Argentine used to win the 'breaker’ 7-5. With the help from the computer, Del Potro was, for the first time, in the match.

In the third set, Federer complained to the umpire, Jake Garner, that Del Potro was taking too long to decide whether he was going to challenge a call or not. When Garner seemed to suggest that Federer should stop complaining, the microphones picked up the Swiss telling the official: “Don’t tell me to be quiet, okay? When I want to talk, I’ll talk. I don’t give a s*** what he said.”

Del Potro's fitness and ability to last five sets at the highest level had remained about the only question mark hanging over his game going into the final

Staring down the barrel at 15-40 early in the fourth set, he found two huge forehand winners to save, then broke to love for a 3-2 lead, only to see Federer level at 4-4 with some brave attacking play.

Federer was just two points away from the title in game 10 before Del Potro came storming back to earn break points in game 11.

But a pulsating encounter would require another tie-break.

There was more bad feeling over the use of Hawkeye but it was two missed forehands from Federer that allowed Del Potro to take the match into a fifth set.

In the fifth set Federer’s legs grew weary. His double-faults mounted. He could not figure out a way to stop the 6-foot-6 del Potro from pounding forehands past him.

Federer had one chance in the to get back on serve but put a backhand long, and from then on Del Potro played nervelessly.

He reached two championship points on the Federer serve in game eight, converting the second when Federer hit a backhand long.

The sixth-seeded del Potro came back to win his first Grand Slam title by upsetting the No. 1-seeded Federer 3-6, 7-6 (5), 4-6, 7-6 (4), 6-2.