Susan Boyle sings for 25m viewers on America's Got Talent Rex

SUSAN BOYLE wowed audiences as she made her US debut on Wednesday night, performing at the final of hit show America's Got Talent.

The singer, who rose to fame earlier this year when she bowled over the judges on Britain's Got Talent, chose an unlikely song for her first performance - a Rolling Stones cover.

Boyle is making her first ever visit to the US this week and was mobbed by photographers and more than 1,000 fans when she landed in Los Angeles.

Her appearance, singing Wild Horses from the Stones' Sticky Fingers album, will have been one of the most keenly watched shows in the US with all eyes on the outcome of the hit series.

Boyle, 48, found fame across the Atlantic well before her arrival in LA when millions viewed her BGT performance on YouTube.

America's Got Talent host Nick Cannon called her "a singer who took the whole world by storm just a few short months ago".

"She was launched on an extraordinary journey to take her to unprecedented global fame overnight," he added.

Backed by a pianist, string section and a tuxedo-clad choir, Boyle appeared in a black gown with her hair straightened for her US TV appearance.

The singer was given a standing ovation by the studio audience and judges, who included Sharon Osbourne and Piers Morgan.

"Wow, truly amazing," Cannon said after her performance.

Speaking on the show, Boyle talked about her spell in the Priory clinic after the pressure became too much following the BGT final, in which she lost out to dance group Diversity.

"I don't remember much about it after the final. All I remember is being put in an ambulance and taken to this clinic.

"I've never felt so tired. I look back on it now and it was a necessity because I was tired. I don't know what was wrong with me though."

She continued: "I used to be a spectator looking out at the world and now I am part of that world and, although frightening, I want to embrace it because I feel a bit more confident within myself right now, more able to cope, more able to take part in the dream.

"I'm ready to get there and get on with it now. I'm not the wee frightened wee lassie I used to be."

Last night's final was won by country singer Kevin Skinner, a chicken farmer, who received one million dollars and a headline slot in Las Vegas and was reduced to tears by his victory.

Britain's Leona Lewis - a former X Factor winner - also appeared on the show.