The Irish teenager faltered part-way through her performance of Hanson's 'MMMBop' and looked noticeably disappointed as she continued with the rest of the track.
When judge Louis Walsh asked Devlin why she "messed up", the 17-year-old revealed: "I've been backstage about to throw up all night."
However, Devlin's admission didn't warrant any sympathy from Tulisa Contostavlos, who said: "You look really upset. I think you know the mistakes you've made today... I did find it quite mediocre at this stage in the competition. I know you're capable of more."
Barlow agreed that the performance had been "a real mess" and noted that Devlin had also forgotten the words to her Jackson 5 tribute on Club Classics night three weeks ago.
"I do feel sorry for you but... the song didn't work for me," he added.
Even Devlin's mentor Kelly Rowland seemed to believe that the performance had failed, but reminded the young star that she was "a fighter" capable of going far in the competition.
Speaking on The Xtra Factor, Devlin revealed just how close she had been to vomiting on the X Factor stage.
"I had to go, 'Oh God, swallow it', but then I went, 'Oh wait, I'm still singing'," she said. "I had to try and jump in, but I didn't want to throw up on television at the same time."
Devlin received a more postiive reception for her second performance, a cover of 'Under The Bridge' by her musical heroes the Red Hot Chili Peppers.
The X Factor continues Sunday (November 27) at 8pm on ITV1.