She performed her cover of Wild Horses by the Rolling Stones on America's Got Talent: The Champions on Monday night.
Boyle received the show's highest accolade when judge Mel B pressed her golden buzzer to put the singer straight through to the finals.
The Spice Girls star described Boyle's voice as "angelic".
"What an absolute honour and pleasure it is to be sitting here and listening to you and your angelic voice," she said.
"And I want to be the woman who gives you something you deserve," she added, before pressing the buzzer.
Boyle, 57, came second on Simon Cowell's Britain's Got Talent in 2009, behind winning dance group Diversity.
Her first audition, a rendition of I Dreamed a Dream from Les Miserables, famously stunned the audience and judges alike.
Since the show, the West Lothian singer has sold more than 20 million albums and had two Grammy nominations.
America's Got Talent: The Champions brings back famous contestants from both the UK and US versions of the show over the past few years.
It marked something of a comeback for Boyle, whose last album, A Wonderful World, was released in 2016.
British teenager Courtney Hadwin, who was a recent America's Got Talent finalist, is also set to make an appearance, as are BGT winners Lost Voice Guy and Paul Potts.
Before Boyle's performance, viewers were shown original content from her first audition and life before BGT.
As she took to the stage, Cowell joked, "What's your name?", before adding, "God, this brings back so many memories."
Boyle replied: "It's great to be back." She then got a standing ovation from the audience for her performance.
Cowell told her afterwards: "I cannot think of any other contestant who has defined this show better than you. You are the one.
"You made a huge difference to a lot of people's lives and I am absolutely thrilled you are here."