X Factor judge Kelly Rowland took her seat back on the top table and warned the other mentors she is back in business and they "aren't going to know what hit them".

The singer returned to the competition after missing last week's live shows because of a virus which prevented her from flying out of Los Angeles.

It followed an on-screen row with fellow judge Tulisa Contostavlos, and her no-show led to speculation that she might be on the verge of quitting.

The judge, wearing a floor-length fuschia pink dress, said: "I'm back and I mean business. These judges aren't going to know what hit them. I feel wonderful, I am so happy to be back in the UK celebrating with the X Factor tonight."

Host Dermot O'Leary asked Contostavlos if the judges were all "happy families again tonight". She replied: "Everyone is happy, we are good, it's about the contestants tonight, not the judges. Everyone is fine."

The first up of Rowland's acts was Irish teenager Janet Devlin, who strayed away from ballads for the first time this week to sing I Want You Back by the Jackson 5. However, it did not go as planned for the singer, who slipped up on her words and received mixed reviews from the judges.

Contostavlos said: "I know I've kept putting pressure on saying I'd love to see you do something up-tempo but I think I'm starting to see that you've kind of got your own style and it's amazing and it's unique and there's nothing wrong with that. Watching you sing something else tonight made me think maybe that's not right for you, maybe you should stick with what you know."

Gary Barlow said: "Janet, I feel really weird saying this but for me that performance just wasn't right tonight. I thought vocally it was really weak, I think you completely lost your identity."

The best comments of the floor fillers-themed night were for Scouse star Marcus Collins, who sang Jackie Wilson's classic Reet Petite. Barlow hailed his rendition as the "performance of the season". Louis Walsh said: "That was your best performance yet. You are the perfect pop star. You can sing, you can dance. You are the X Factor, 100%."

The nine hopefuls will find out their fate in the results show on ITV1 on Sunday, with two facing the boot. Collins is the new favourite to win the competition following his performance, bookmaker's Coral said.