The shy church volunteer gave a rousing, but occasionally nervous, performance on the "American Idol"-style show "Britain's Got Talent," with a version of the song "Memory" from the musical "Cats."
Members of the public voting in a telephone poll picked her as the best of eight performers who appeared Sunday, meaning she will sing again in the contest's final next Saturday.
Flashing a broad smile, Boyle danced in delight as results were announced and said had relished the chance to perform. "Fantastic, absolutely fantastic," she said. "What pressure? I've really enjoyed myself tonight."
Wearing a plum colored beaded dress - and a touch more makeup than during her last performance - but with the same unruly shock of hair, Boyle overcame early jitters to deliver a powerful vocal.
Producers said the 47-year-old's appearance was being posted on the Internet almost immediately, after about 60 million people watched her last performance via YouTube.
In her first performance last month, judges who'd raised eyebrows at Boyle's dowdy image were won over by her bold voice and surprisingly confident performance of "I Dreamed a Dream" from the musical "Les Miserables." The sometimes awkward looking Scot won praise from celebrities, including Oprah Winfrey and Demi Moore, and even won a name check in her favorite cartoon "The Simpsons."
On Sunday, the show's judges and audience rose to their feet to applaud, but those posting comments to the Twitter Web site appeared divided. While some hailed her performance, others appeared underwhelmed.
Bookmaker William Hill has made her a runaway favorite to win on May 30.
Contestants are competing to perform at Britain's annual Royal Variety Show - attended by members of the royal family - and win a 100,000 pound ($159,000) prize.
The singer, who lives alone with her cat Pebbles in one of Scotland's poorest regions, said before Sunday's performance that she wouldn't transform her appearance. "I just want people to see me for who I am, and do my best at singing the song, that's what I am focusing on," she said.
Boyle, who says she's never been kissed, grew up the youngest of nine children in Blackburn, a community of 4,750 people 20 miles (32 kilometers) west of Edinburgh, in Scotland, and a district blighted by unemployment and crime. She suffered learning difficulties as a child and was bullied by other children.
As an adult, she's struggled for work but had been a regular on her local karaoke circuit and performed in church choirs.
In an interview with The Associated Press at her home last month, she said the death of her mother had inspired her to enter the TV talent show.
"I wanted to show her I could do something with my life," Boyle said.
Click here to see her performance of "Memory" on YouTube.