The X Factor finalists have battled it out to save themselves from being booted off the reality show after it was revealed that four acts will be sent home.
The 16 hopeful acts each had the chance to sing a track on the Britain vs America themed show.
Judges Gary Barlow, Louis Walsh, Tulisa Contostavlos and Kelly Rowland will have to make the agonising decision to each lose one of the acts they have been mentoring.
Although the judges were not vying for the public vote, the claws were out on the panel with Contostavlos and Barlow rowing about some of the performances.
The former N-Dubz star told Barlow that she was going to show him her feisty side and called him "mental" after he expressed a critical view of boyband Nu Vibe.
After their rendition of Chris Brown's Beautiful People, Barlow told the group: "I thought the song choice was good in a way that you could actually hide behind that song.
"I feel like I didn't really hear any of you sing together. I felt like I was watching five solo artists other than a band."
Contostavlos, who is mentoring the groups throughout the contest, interjected: "People have been waiting for my feisty side to come out in this show and here it is - you must be mental.
"These boys are the next generation of boyband and they are going to blow people out of the water."