The 41-year-old judge took Sones aside ahead of tonight's show (October 20) and critiqued his performance of Rihanna and Eminem's 'Love the Way You Lie' on last week's show (October 13).
Watching Sones's performance back, his mentor Barlow said: "Right now listen, I'm going to be really honest with you. Let me critique this for you. Flat. Flat. Flat. Flat.
"We're a minute in, 12 flat notes. I'm not going to play any more. There's 32 flat notes in that two-minute performance. That was awful. You're going downhill."
Sones replied that the criticism was "what he needed".
Following his performance tonight, judge Louis Walsh said: "That was the perfect performance, I think you've got your mojo back", with Tulisa adding: "Last week, we all felt like something was missing. Whatever that was is back this week. There's only one way to go, and that's up."
Barlow then responded to the comments he had made to Sones earlier in the week and apologised, saying: "I'm sorry to have been so hard on you."
Host Dermot O'Leary said that he thought Barlow's tough assessment of his own act was "weird", before asking the judge why he was so hard on Sones. Barlow replied: "Kye's very talented and I knew he would take it in."
Photo gallery - The X Factor's Club Classics week:
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