Cowell, who is mentoring the girls’ category for the first time, told 17-year-old Samantha Lavery to “peel away the mask” during performances at the judges’ houses.
The most intense stage of the show saw the girls travel to Simon’s house in Malibu, California whilst Louis Walsh’s groups visited Ibiza.
Cowell was roundly criticised by Bunton and Mel B who were helping him narrowing his seven acts into a final three, after his comments to the teenager.
He told Lavery: “I kind of wish we had met without what you think is your pop-star image. I think that with you we have had a bit of a mask put up. All I’m saying Sam is I want to peel away the mask.”
Cowell then turned to Mel B and Bunton and asked if his remarks were “bad”, with Bunton telling him the youngster was “allowed to experiment” and Mel B adding: “It is bad... that’s what kids do.”
He told a visibly shocked Lavery he “wanted to get to know who you really are”, adding “maybe you should come back”.
After she departed Cowell told the former Spice Girls: “I would just like for her take all the make-up off, come in a pair of jeans and just sing.”
Lavery returns at the end of the episode, with Cowell calling her performance of Ed Sheeran’s Make It Rain “powerful” before adding “it was like we were meeting you for the first time” and saying she was “brave” for coming back.
Caitlyn Vanbeck’s rendition of George Michael’s Praying For Time was also interrupted after the 18-year-old momentarily forgot her lyrics.
Walsh, who was joined by Alesha Dixon and X Factor 2014 runner-up Fleur East, once again battled over his choices for the live shows after last week’s Six Chair Challenge chaos.
Novelty act Ottavio and Bradley’s entertaining cover of Christina Aguilera’s Candyman left Walsh, Dixon and East in hysterics, with Ottavio capping the performance by pushing his bandmate into the pool.
Three-piece 5am’s throwback to R.Kelly’s She’s Got That Vibe wowed Dixon who told Walsh the boy band were “just going to get better” but she was less impressed with wildcard Yes Lad who she called “corny” after their performance of Michael Jackson’s Don’t Stop Til You Get Enough.
Cowell, who was confronted with a provocative rendition of Aguilera’s Genie In A Bottle from 18-year-old Soheila Clifford, also wrestled with his choices, saying he wanted to put through five of his seven acts.
“I made the show up, there’s no rules”, he told Bunton and Mel B.
Also appearing on Saturday night’s show are couple Tom and Laura, girl groups Skarl3t and Four Of Diamonds, Olivia Garcia, Kayleigh Marie Morgan, and return contestants The Brooks, Emily Middlemas and Gifty Louise.
:: The X Factor continues on ITV on Saturday at 8pm.