By Tuesday, a video clip of Boyle's performance on Internet site YouTube has been watched more than 2.7 million times.
Watch the performance HERE
The unemployed Scot who said she'd "never been kissed" drew titters when she told the judges her ambition was to be a professional singer.
But her soaring rendition of "I Dreamed a Dream" from the musical "Les Miserables" astonished the show's hard-to-please judges.
They were captivated by the singer from Blackburn in western Scotland. Usually acerbic judge Simon Cowell dubbed her singing "extraordinary." Fellow judge Piers Morgan said her "stunning" performance was "the biggest surprise I've had in three years of this show."
The show, the first in a new series of "Britain's Got Talent," was watched by 11.4 million of Britain's 60 million people on Saturday night.
British bookmakers made Boyle the early favorite to win the series.
She is the latest in a proud tradition of underdogs who win the heart of the British public.
"Britain's Got Talent" made a star of its first winner, an unassuming mobile phone salesman named Paul Potts. He wowed audiences with his rendition of the aria "Nessun Dorma" and has become a global recording star since winning the series - and signing to Cowell's record label - in 2007.
The program, produced by Cowell, is the sister show of "America's Got Talent." Both are old-fashioned talent shows that resemble the singing contest "American Idol" but with the addition of dancing, comedy and other forms of performance.
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