Louis Walsh's last remaining act found herself in the bottom two during tonight's show alongside Misha B, who is mentored by Kelly Rowland.
Brucknell gave a heartfelt rendition of Judy Garland classic 'Over The Rainbow' as her safety song, while Misha B chose Jessie J's 'Who You Are' for the sing-off.
In the judges' vote, Dermot O'Leary first came to Walsh, who described the sing-off as featuring "incredible, emotional performances from two amazing girls", but ultimately backed his own act.
Tulisa Contostavlos similarly called both girls "amazingly talented" and said that they had given "one of the most dramatic sing-offs ever". However, she chose to save Misha B, saying that the 19-year-old was "the person I can relate to as a musician and whose album I would buy if it got released".
Rowland, like Walsh, chose to save her own act and urged fans to vote for Misha B next week.
She said: "I really believe in this young lady... I think you are a great talent, Kitty, but I really, really see a bright future for Misha."
The deciding vote was left to Gary Barlow, who noted that both girls were probably the most determined acts still in the competition.
"Kitty, I've always been a huge fan of yours," he said. "[But] the connection between you and the audience, it just doesn't seem to be there and it's got to be the likeability factor, because you sing and perform really well."
After arguing that Misha B was the act most likely to be signed by a record label, he cast the third and final vote for Brucknell.
> Lady GaGa comforts Kitty Brucknell after 'X Factor' exit
Speaking to O'Leary after the result, Walsh claimed that Brucknell was "one of the best people [he'd] ever mentored" and called for her to receive a recording contract.
"This girl wants to be a star," he said. "She loves music, she loves performing and I do not want it to end now for her."
Brucknell bowed out of The X Factor by taking O'Leary's microphone and singing the chorus of Lady GaGa's 'Born This Way' as the audience cheered.
The X Factor returns next Saturday at 8.15pm on ITV1.