She was working as a waitress in a cocktail bar: now she's America's idol

The star-making mania that swept ITV's Pop Idol to success was replicated in America when a 20-year-old former cocktail waitress with a thumpingly powerful voice became the first "American Idol".

As in Britain, the ratings figures soared over the life of the series, with the show's panel of judges sorting the musical wheat from the chaff and slowly focusing on the handful of genuine talents among the original pool of 10,000 entrants.

More than 18 million people watched the penultimate episode, and Wednesday night's finale was estimated to have attracted in excess of 20 million.

The last two finalists were Kelly Clarkson, the small-town Texan who went on to win, and Justin Guarini, a pompom-haired salesman from Pennsylvania with a more silken, laid back vocal style. Ms Clarkson was declared the winner by an avalanche of phone-in votes, and she had to fight back the tears as she belted out a celebratory rendition of "A Moment Like This, one of two songs written specially for the show. As in the British model, she will now be given a manager, a recording contract and mountains of free publicity.

The last night of the show, which aired on Rupert Murdoch's Fox network, was a glittering showbiz affair, broadcast live from the home of the Oscars, the Kodak Theatre in downtown Hollywood. The enormous success came as something of a surprise to Fox executives, who had regarded it as a cheap summer-time filler and unlikely to match its British counterpart.

A key component in the mix was British judge Simon Cowell, the one transplant from the original series, who delivered his withering verdicts on everyone and everything and rapidly established himself as the compulsively watchable man you love to hate. As the series came to a close, Fox announced that he had been offered a $1m contract to stay on for a second series, which might air in January. Mr Cowell responded to the offer in characteristic fashion, taking time to praise the American series but gently bashing the Brits at the same time.

"I have to begrudgingly admit that the talent in the US is better than in the UK," he said. "It's nothing derogatory about Will [Young, the British winner]... I just thought the overall talent in the American Idol Top Ten in the end was better than the British Pop Idol Top Ten. There's 50 million people in England and 250 million people here."

Over the next few weeks, America will be subjected to more Idol-mania, as Ms Clarkson's first single is released and the 10 official finalists from the show – Ms Clarkson, Mr Guarini and eight others who made the final cut – go on a national tour. Ms Clarkson has also been asked to sing the American national anthem at the 11 September memorial concert.

Simon Fuller, the management mogul who steered the Spice Girls to success, is to add Ms Clarkson and Mr Guarini to his books. It is a measure of the success of the show that Mr Fuller has reportedly been invited to meet President Bush.