The first time during the tournament he had lost his serve, the first time he lost a set, the first time a spouting water hose had ever interrupted him, but this was not the first time that David Nalbandian had contrived to introduce inklings of uncertainty into the mind of Roger Federer.

Nalbandian, who had suffered a year of frustration and lack of fulfilment, stunned the world No 1 - but clearly not himself – with a 1-6, 6-3, 6-3 victory in the Mutua Madrileña Masters final at the Pabellón de Cristal that reestablished the 25-year-old as a force to be reckoned with. It is just what Great Britain’s Davis Cup squad least wanted to hear about – another resurgent Argentinian.

Nalbandian had spent the best part of the year hanging around the periphery of the leading tournaments, having reached one quarter-final in 15 tournaments, at the relatively humble event in Barcelona in April. After Wimbledon, he teamed up with Martín Jaite, the former Argentina Davis Cup player, and put his physical conditioning into the hands of Fernando Cao, who has been responsible for knocking Guillermo Cañas and Fernando González into prime condition.

It was long felt that Nalbandian was held back by carrying a few more pounds around his girth than a potential grand-slam tournament champion ought. Those have been shed, along with the inhibitions that stymied him earlier. His form in Madrid has been exceptional, recovering from a set and 4-0 down to beat Tomas Berdych in the second round and yesterday joining Boris Becker in 1994 and Novak Djokovic in Montreal this summer as the third man in the history of the ATP Tour to defeat the world’s top three ranked players in succession to win a title.

When Federer pocketed the first set in half an hour, another victorious outcome appeared probable. Even the line-calling technology blew a fuse when Nalbandian questioned a serve by Federer. It seemed that nothing would go right. But once he began to play with enough aggression to pin back Federer and strike out with his customary unerring line and length, Nalbandian took a grip from which the Swiss could not escape.

It will make little difference to Federer’s end-of-season plans. He goes to Basle this week to keep his home-town fans content, is expected to play a part in Paris the week after and then defend his Masters Cup crown in Shanghai. “I don’t practise as hard as I used to,” he said. “There is not much point trying to improve your game after the US Open, it is about staying healthy and being ready for the new year to begin.”

That new year – and the old challenges, especially to enhance his clay-court game – is uppermost. Federer will add the Estoril Open in Portugal to his schedule for 2008.