The 47-year-old church volunteer performed a version of the number "Memory" from the hit musical "Cats" to a rapt audience during the semi-finals of the show.
A confident Boyle was voted the viewers' favorite in a telephone poll, allowing her to sing in the show's final next Saturday.
After an initially inauspicious start last month when she gave her first performance on the show, Boyle overcame jibes about her somewhat frumpy appearance to astonish the show's judges and audience members with her soaring voice. She has since become a sensation around the world.
A smiling Boyle danced with glee after Sunday's performance, telling judge Piers Morgan, "This is for you Piersy baby." Morgan responded, "You look absolutely beautiful and you sang well. When the world was going through a tough time you provided a bit of happiness."
Fellow judge Amanda Holden expressed her relief that it all "went well. I was biting all my plastic nails off. It was fantastic."
Even the usually cutting Simon Cowell could find no fault with the woman once dubbed the "hairy angel" by the British tabloid press. Cowell told Boyle that she was "one special lady," adding, "I want to apologize for the way we treated you the first time you sang. You made me and everyone else look stupid."
Amid mounting speculation over how far Boyle would change her appearance to meet the demands of her growing fame, the singing star turned up to Sunday's performance in a dark plum-colored, beaded dress, wearing more make-up than last time, but with the same unruly bob that made her famous.
In an interview that aired on the TV show "Extra" Boyle said she had no intention of transforming her appearance. "I wouldn't like to change anything," she said. "I'm perfect the way I am."
Susan Boyle Odds-On Favorite to Win Contest
Boyle watchers certainly seem to think so, with bookmaker William Hill making her an odds on favorite to win the competition on May 30. If she wins, she will be invited to perform before Queen Elizabeth II at Britain's annual Royal Variety Show, and will take home prize money worth $159,000.
It's all a long way from the Scottish village of Blackburn, where Boyle lived alone with her cat Pebbles.
"I've never had a boyfriend," she told judge Cowell," "I've never even been kissed."
Villager Jackie Ruffel, who manages the Happy Valley Hotel, where Boyle is a pub regular, told ABCNews.com that Boyle primarily "took care of her mom. The rest of the family all got married and moved away, but Susan always remained in the house looking after her mother. When her mom passed away, she kind of withdrew into herself."
According to the British media, Boyle's mom Bridget always encouraged her daughter to take part in regional singing competitions. Boyle also performed in her church choir from the age of 12 and, when she was older, sang karaoke in local pubs.
Afterward, Boyle signed up for singing lessons with local voice coach Fred O'Neil and in 2000 she sang "Cry Me a River" for a charity CD, her only previous recording. Last August, when she heard about auditions for "Britain's Got Talent," she decided to go for it.
Her singing has won her many fans, including her idol, British theater legend Elaine Page.
"She's a country girl, and I think she just has the most lovely, natural voice," Page said on "Good Morning America." "She's very open in her performance. ... In such gloomy times that we're all sort of living through at the moment, economically speaking, she was a breath of fresh air."
Even as some in the media have speculated if Boyle may be too good to be true, Ruffel insisted, "She's definitely the real deal, sweet innocent Susan."
But Boyle confessed in her interview with "Extra" that she was just joking when she told Cowell that she had "never been kissed."
"It was meant as a joke," she said. "I've got a wicked sense of humor, you know!"
Friends Say Boyle Unchanged by Fame
Still, British cultural critic Shane Watson said the fuss over her comments was unwarranted.
"The point is, even if they do groom her up -- and why not -- and even if she was joking when she said she'd never been kissed, it doesn't detract from the fact that she is an ordinary woman, unglamorous, unmarried, unsophisticated, unworldly, and of a certain age, and as such she is a breath of fresh air," Watson told ABCNews.com.
Ruffel said the attention hasn't changed her friend at all.
"She's still Susan," she said. "She was in here the other day, and we were saying to her, 'Finally you made it.' And she said, 'I don't know what all the attention is about, I just wanted to sing."
"You won't change Susan," added Ruffel. "We have a saying here: You can take the girl out of Blackburn, but you can't take Blackburn out of the girl. She'll stay the same with her feet firmly on the ground, a sensible girl."
After the results were announced on Sunday night, Boyle said she felt "fantastic," adding, "What pressure? I've really enjoyed myself tonight."
The Associated Press contributed to the reporting of this story.