In a post-show vote by fans, Boyle was bested by the 11-person street dance group Diversity, which performed a high-energy dance number that got the crowd and the country roaring.
Boyle fell back on familiar territory, performing "I Dreamed a Dream" from the musical "Les Miserables."
In April, Boyle's rendition of the same song made her an overnight global sensation. Tens of millions of people online watched the spectacle of the 48-year-old singer appearing out of place and unlikely to impress the judges or the audience, her attire frumpy, her haircut no-nonsense. Instead, she shocked the world by belting out the show tune favorite and commanding the stage.
Her unexpected performance got her on "Oprah" and "Larry King Live," and even won her accolades from London stage veterans like Elaine Paige and Hollywood power couple Demi Moore and Ashton Kutcher.
Diversity, from the suburban county of Essex, east of London, performed flawlessly. Their performance, a mix of break dancing and choreographed artistry, brought the judges and the crowd to their feet.
Judge Amanda Holden, a television host, told the group, "You have left me speechless. I think you've blown Flawless [another street dancing troupe in tonight's final] out of the water."
The crowd mostly cheered, but loud boos could be heard from supporters of other performers.
Simon Cowell, the notably ascerbic judge on "Britain's Got Talent" and the U.S. performance show "American Idol," gave a definitive blessing.
"All bets are off," he said. "This is the only performance tonight I would give a 10 to."
He called the choreography "sheer and utter perfection."
Talent agent Dane Millard said Diversity may have profited by the fact that it was the second-to-last act. However, Millard says of all the acts, "theirs was the best of the evening.
"Diversity had inventiveness, wit, energy and flawless execution," Millard said. "I could see them on tour soon and/or doing support dancing for any talent in the world."
Boyle's performance tonight came after a hard week for her. The church volunteer from Broxburn, Scotland -- population 14,000 -- was caught on camera last Wednesday gesturing obscenely at a pair of reporters and reportedly was overheard by police shouting "How f***ing dare you! You can't f***ing talk to me like that."
Critics and detractors assumed Boyle had cracked under the pressure and reports surfaced that she was not going to make the final.
London's The Sun tabloid, never a newspaper to pull a punch, led with the headline "SuBo Goes Loco" the following day.
In tonight's performance, Boyle glowed. Her silver sequined gown draped to the floor, her demeanor was confident and fully in control -- in every way a diva. Her performance garnered a standing ovation from the audience and the judges.
Judge Piers Morgan, who appears to have become one of Boyle's supporters, told her, "You've had a very difficult week boiling over, cracking up. All I kept thinking about was that all you had to do was sing the song you sang before. That to me was the greatest performance I have seen in any 'Britain's Got Talent.' You should win this competition."
Boyle beamed. The crowd cheered and jeered.