The show let viewers choose which songs the remaining contestants should perform for one of their slots - and they also performed an acoustic track of their own choosing.
And it was Carly Rose's version of Justin Bieber's As Long As You Love Me that stole the show, with LA Reid telling her it was her best performance of the series so far and Demi Lovato saying she did the track better than Biebs.
Simon Cowell told her: "I am seeing a star emerge in front of me."
Her second song - chosen by the public - was a cover of Beyoncé's If I Were A Boy - and gained only slightly less enthusiastic praise from the judges.
Other show highlights included Tate Stevens going from country to rock with a cover of Bon Jovi's Livin' On A Prayer and CeCe Frey getting her act together with an unplugged version of Lady GaGa's The Edge Of Glory.
The results show will be screened tonight in the US.