David Nalbandian upset world number one Roger Federer to win the Madrid Masters on Sunday, the Argentinian's first ATP title since May 2006.

Federer, the reigning champion, looked well on course to claim the 52nd singles crown of his illustrious career after cruising through the first set, but unseeded Nalbandian hit back to claim a 1-6 6-3 6-3 victory in one hour 48 minutes.

Nalbandian, who has now beaten all top three seeds in Madrid after knocking out Novak Djokovic and Rafael Nadal in the previous two rounds, last reached an ATP final in Estoril, Portugal 18 months ago, when he beat Nikolay Davydenko.

That triple success over Nadal, Djokovic and Federer was only the second time since Boris Becker in 1994 that a player had beaten the top three in the world in consecutive matches.

Djokovic himself also managed it earlier this year after defeating Andy Roddick, Nadal and Federer in Montreal.

Nalbandian, the 2004 runner-up here, was gracious in victory, saying: "Roger, you are without doubt the best and I hope that you continue like that and you have a good end to the season."

Nalbandian was third in the world just 18 months ago, but he has slumped down the rankings and started the Madrid Masters in 25th spot, having reached just one quarter-final this year.

But he has a decent record against Federer down the years, with the Swiss ace having only held an 8-6 advantage over the South American.

Nalbandian won their first five meetings, but Federer soon got the measure of the Argentinian, winning eight of their previous nine clashes before Sunday.

"He's one of the guys I've lost most against on tour, I don't know if I've lost to anybody more, maybe (Lleyton) Hewitt, so it shows what a great player he is," Federer said.

"He struggled sometimes early on in the tournament, but when he gets through the first few he started to play very well.

"I didn't play my best, he was the better man today.

"I though I was more aggressive in the first set, and he was more aggressive in the next two sets. I was really struggling to play aggressive and after that first set he played more tough, more long, he didn't miss that many balls anymore and I just couldn't play the way I wanted to.

"It was a bit of pity and a bit disappointing, but he really played a great tournament, he beat great players beforehand so I knew it was going to be a tough match."