In front of a Wembley Arena crowd of 10,000 screaming fans, Amelia belted out Christina Aguilera's Ain't No Other Man, before taking to the stage with mentor Kelly Rowland for an impressive rendition of River Deep, Mountain High.
Gary Barlow admitted that he was concerned about how the 17-year-old would make the transition from the TV studios to Wembley but said, "You did it beautifully."
Louis Walsh was also impressed, telling Amelia, "The public voted you back and I see something raw and something amazing - it's all about the potential with you."
Hmm... makes a change from, 'it's all about the voice', at least.
There were no tears from Amelia as Dermot announced that she would be leaving the show.
She thanked fans for giving her a second chance on the show and added, "My ambition was to get to the final and I did it.
"And this isn't the last of Amelia Lily! Tonight was the best night of my life and the best moment was performing with Kelly Rowland herself."
Kelly declared she now had an "incredibly bright" future.
Last night's "biggest X Factor final ever", kicked off with Dermot's longest dance sequence ever - an on-location, Austin Powers-inspired journey through London featuring oddball Goldie Cheung.
Marcus Collins opened with his first song, Outkast's Hey Ya, aboard a giant jumbo jet surrounded by air hostesses. He got a standing ovation from the judges for his efforts too, with Louis declaring him a "born pop star" and Tulisa saying, "The hard work and the determination paid off!"
His second performance ditched the big production in favour of Gary Barlow, a piano and Billy Joel's She's Always a Woman (dedicated to his mum... awww).
Current favourites Little Mix began their final with Candi Staton's You Got The Love. The judges were impressed - Kelly called the girls "incredibly special", Gary pointed out that it's hard to believe they didn't even know each other three months ago and Louis is absolutely determined to get "Girl Power back in the charts".
Then it was time for Tulisa to join her 'little muffins' on stage... and their combined mash-up of Alicia Keys songs If I Ain't Got You and Empire State of Mind sent the audience into a frenzy.
As Gary Barlow said, "It's anybody's final".
Marcus and Little Mix will do battle again tonight.