But Cheryl Cole pulled it out of the bag, delivering a slick rendition of her new single Fight For This Love on Sunday evening.
The 26-year-old earned rapturous applause and high praise from fellow judge Simon Cowell, who said: "Much as it pains me to say this, that was incredible."
Despite confirmation from the show's bosses that she would pre-record her segment, Cheryl performed live. Striking in a military-inspired outfit, the Geordie lass put on a Janet Jackson-esque routine flanked by a troupe of backing dancers.
She sang the first part of the song, though appeared to lip sync the latter section of the track.
And athough she had said there would be no friends or family watching, her Girls Aloud bandmates Kimberley Walsh, Nicola Roberts and Sarah Harding were there to cheer her on, as was husband Ashley Cole.
Meanwhile, making her first UK appearance in 12 years, Whitney was also a class act. Not even a wardrobe malfunction – the back strap on her glittering floor-length gown came undone – could take the shine off her performance.
"I sang myself out of my clothes," she told host Dermot O'Leary after belting out her new single Million Dollar Bill.
The Sunday night show was the end of the road for one of the acts Cheryl mentors. Scottish singer Rikki Loney lost out in the sing off against Rachel Adedeji, who was in the bottom two for the second week running.
Simon cast the deciding vote, and went with Rachel, saying her performance of U2's With or Without You was better than Ricky's rendition of Flying Without Wings by Westlife.