Cocozza, who was in the sing-off with Nu Vibe last week, was saved by viewers after his performance of Primal Scream's 'Rocks' yesterday.
However, Barlow said on The Xtra Factor that tonight's bottom two - Kitty Brucknell and eliminee Sami Brookes - was a "big shock" for him.
"Me and Frankie were backstage honestly holding each other," he admitted. "I was convinced Frankie would be in the bottom.
"Because of last week, it was such a big shock. And he's been so nervous this weekend, so we were both preparing ourselves for it. So it was a massive shock it was Sami and Kitty."
Barlow also suggested that the public has not yet seen everything Cocozza has to offer.
"Frankie's a star, whether you like it or not," he said. "I'm so glad for him he stayed in this week, I really am. I think people slightly have the wrong view of Frankie, actually. I think we're still yet to see the real Frankie. He likes to go out, he likes to party, he's a teenager.
"But he's very serious when it comes to learning his songs. I'm very proud of him. There's another side I want people to see."
The X Factor continues on Saturday at 8pm on ITV1.
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