Standing motionlessly at the back of the stage, Hadwin quietly gestures for the music to kick in, and the judges were somewhat surprised when the opening chords of "Hard to Handle" by Otis Redding rang out through the theater.
In the audition, Courtney initially comes on stage and awkwardly answers judge Mel B's questions. Before she was even done, the audience was on their feet. "Oh my gosh. You are not from this era", he says seeming disappointed he can't offer her a record deal there and then. "You're like this shy little thing when you first came out".
Courtney Hadwin gets the golden buzzer and she moving straight to the live shows. Mandel said, just before hitting the golden buzzer.
She went on to reach the final of the series in 2017 - but lost out to fellow singer Jess Folley.
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Host Tyra Bank adds: "You were absolutely awesome. I've never seen anything like that", host Tyra Banks said of her performance.
She's not the first British act to do well in America's Got Talent, with Wimbledon ventriloquist Paul Zerdin winning the 2015 series.
She tweeted her thanks Tuesday night.
Courtney had previously been a finalist on The Voice Kids UK, but has gained plenty of new fans - Twitter exploding after her performance.
America's Got Talent airs Tuesdays at 8/7c on NBC.