The schoolgirl from Peterlee will now be in the running for the $1m (£750,000) prize money on the NBC show.
"Bloody hell, Courtney", Simon Cowell said.
In the audition, Courtney initially comes on stage and awkwardly answers judge Mel B's questions. That changed her life.
When "Hard to Handle" blared from the speakers, she began thrashing around the stage while belting out the song in her rich and soulful voice.
Both the audience and the judges are left open-mouthed with surprise at the unique performance.
"You are not from this era".
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However Howie was so floored he said: 'The only thing I can do for you young lady...' as he dramatically launched an arm up and smashed the buzzer, while the other judges lost their proverbial. "You are not from this era, you are from whole different era", said Howie. Mandel says as he strikes the buzzer on the judges' desk.
"I can't sign you to a record deal".
"That's talent", host Tyra Banks declared backstage during Guthrie's performance.
She tweeted her thanks Tuesday night.
Before coming to 'America's Got Talent, ' Hadwin previously competed on 'The Voice Kids UK, ' where she made it to the final rounds of competition.
This week her audition from America's Got Talent went on TV and the result was pretty unbelievable!