Demi Lovato and Simon Cowell
11/08/2012 at 10:00 AM EST
The X Factor
's top 13 contestants
(welcome back, Diamond White!) performed songs from movies Thursday night – hoping to earn viewers' votes for the first time this season – but most of the drama came from Demi Lovato
and Simon Cowell
The two clashed
almost right away after Paige Thomas's highly theatrical performance of "Take My Breath Away."
"The beginning was great but I think it needed to go somewhere ... You don't want to turn this into a karaoke competition," Simon told Thomas's mentor. "Madame," he continued, referring to Demi, "could have used a little more imagination in terms of the production of the song."
"I'm so sorry I let you down," Demi said sarcastically. "You did so amazing. It was so beautiful." Then to Simon she added, "Obviously everybody in the audience disagrees with you."
And that was just the beginning! It's no secret that Demi is a fan of Simon's boy banders, Emblem3, but she took a dig at their coach for including a nod to One Direction's "What Makes You Beautiful" in their impressive mash-up performance, which also included Motown classic "My Girl" and Katy Perry
's "California Girls."
"If I had been your mentor, I would have made sure that I wouldn't have plugged one of my artists that you can easily be compared to," she said.
When Jennel Garcia took the stage to sing "I Love Rock 'n' Roll" by Joan Jett, Simon had his turn: "I don't like what Demi has done with the way you look. You are unrecognizable from the person we first saw," he said. "You've got to challenge yourself on these songs ... You are better than this."
"That's why I'm her mentor and you're not," Demi snapped back.
Perhaps the most intense moment of conflict came when Simon warned CeCe Frey that Demi wasn't doing a good job as her mentor.
"This song choice was just horrible," Simon said of Frey's "Eye of the Tiger." "You are being taken in a direction you shouldn't be going into ... You should be making your own song decisions."
Demi asked Frey if she like the song choice and she said she did. "It's important for everyone to see how far you've come," Demi said. "I'm going to help you go whichever direction you want to go."
Even while giving positive feedback to rappers Lyric 145 for their surprising song choice of "Supercalifragilisticexpialidocious" from Mary Poppins
, Demi took a dig at her older costar.
"You guys got me so hyped," she said. "Who knew in [Simon's] rusty old brain there was some fresh, cool, hip thoughts? You guys nailed it."