Teenager Courtney Hadwin debuted new music on America's Got Talent: The Champions.
The 14-year-old, of Heselden, near Hartlepool, shot to fame after reaching the final of the main show last year before signing a record deal with judge Simon Cowell in December.
Courtney appeared on Champions and performed an original song, earning praise from the judges.
She did not immediately reveal the name of the track.
Cowell told her: "That was bloody fantastic.
"Something has changed in you in the time you were on the show last year to now, your interaction with the audience, the confidence, I think this has been my favourite performance of you so far."
Spice Girl Mel B is also on the panel and said Courtney is a "champion".
She said: "You are only 14 and you have already figured out what style to dress, what style of music you like, you have figured out your performance.
"Most people, it takes somebody a lifetime just to figure just one of those things out.
"And now you are among the champions and you are a champion, hands down."
And German supermodel Heidi Klum added: "I love when you come on to the stage and then when you start singing you turn into this lioness and you just roar."
Despite the judges' glowing comments, Courtney did not do enough to progress to the final, making it to the final three before missing out to singer Christina Ramos.
Courtney is now relying on a wildcard to reach the finals.
America's Got Talent: The Champions brings together former winners and standout acts from different versions of the show from around the world.
Also appearing on Monday night was Ashleigh Butler, who won season six of Britain's Got Talent while performing tricks with her dog Pudsey.
Pudsey, a male border collie, bichon frise and Chinese crested cross, died in 2017 and Butler has replaced him with Sully.
The pair performed a routine to Flashdance's She's A Maniac.
Last week, Scottish singer Susan Boyle, who finished second on Britain's Got Talent in 2009, also appeared.
America's Got Talent: The Champions continues in the US on January 21.