Go, go Delpo. A US Open championship that took a lot of time to take flight saved its finest cameos for the last two days as Kim Clijsters offered a whole dimension to Mummy Power and Juan Martin Del Potro, a gentle giant of a young man, stole Roger Federer's thunder in the men's final, cementing his place among the legends.

To beat Federer you have to prove you mean business. After one and a half sets, Del Potro looked forlorn, angry, downcast and well on his way to being beaten, quite probably in straight sets. That was how it appeared from the outside. On the inside, he had never given up the fight and that, against Federer, is very much half the battle.

Last year at the Open, Andy Murray defeated Rafael Nadal of Spain in a semi-final that stretched over two days because of atrocious weather and did not have it in the legs to compete against Federer - over whom he had a 2-1 head-to-head advantage at the time - the next afternoon. Del Potro thrashed Nadal on Sunday for the loss of six games and was thus pretty refreshed, though his record against Federer before yesterday's climax was 0-6.

When Federer got off to his strolling start, was swinging away as only he can, forehands finding their spots, one felt that Del Potro would be in for a Murray-like lesson. But the big Argentine plugged away and forced himself back into the second set courtesy of a Hawk-Eye overrule on a forehand that the linesman called out but the replays determined had clipped the side of the line. Federer was getting hot under the collar and a second forehand winner down the same line simply riled him even more.

Del Potro won the ensuing tie-break and broke first in the third set, only for the five-time champion to respond and claw his way back to move ahead again. The Swiss had never lost a tie break before yesterday at the US Open, but Del Potro took them both and then, thundering through the ball, swept Federer aside in the fifth set to become a grand slam champion at the age of 20.

"When I won the second set, I think if I continuing playing same way, maybe I have chance to win," Del Potro said. "But after, when I lost the third set, going to break up, I start to think bad things. It was so difficult to keep trying to keep fighting but one more time the crowd and the fans helped me a lot to fight until last point. I think I have to say thank you to everyone for that."

And so Federer is stuck on 15 grand slams while Del Potro joins those who have tasted the experience for the first time. The chances are, he will not rest there. Having ostensibly been raised on clay, he is a superb hard court player and his game would transfer well to grass if only he could bring himself to believe more in the surface. After all, at 6'6" with a serve like his, ground-strokes that scorch the surface and the attitude that will have been hardened by this remarkable success, he is a threat everywhere.

At the start of this year, had you offered Federer two of the four slams, he would have taken them. He played in all four finals, don't forget, losing in Australia and America in five set matches to superhuman efforts from Nadal and Del Potro. Give him a setback and he tends to come back stronger. No doubt it will be the same again.