Audiences were shocked when Hannah, 17, was pitted against Miss Dynamix in last week's sing-off as the student had been one of the frontrunners to take the X Factor crown throughout the series.
Coming back to the stage, Hannah gave a soulful and passionate performance of Jocelyn Brown's 'Somebody Else's Guy' leaving the Judges certain they were right to save her from elimination.
"I don't know why you were in the bottom two last week," Louis Walsh told her.
"But I am so glad we made the right decision and saved you. We saved you because you have this amazing, strong, powerful, soulful voice."
Sharon Osbourne praised her "sensational performance", while Gary Barlow gave her a warm "welcome back" after watching her fighting spirit.
He added: "That is how you come back after being in the bottom two. I think you are the most soulful singer left in the competition."
You have this amazing, strong, powerful, soulful voice.
Louis Walsh to Hannah Barrett
But not all the contestants received such high praise from the Judges as Sam Callahan failed to impress with his performance of the Take That covered track 'Relight My Fire'.
"I hated that performance tonight," Gary told him.
"I thought the vocals were really exposed. You're not the best singer in this competition and the problem for you is that everyone else is just so much better.
Nicole Scherzinger added: "You have so much charisma, so much likeability, so much energy but unfortunately that song exposed your weaknesses vocally.
"Your voice actually sounded smaller than it ever has and more nasal."
But while Sharon agreed with her fellow panellists, she praised Sam for his commitment and hard work.
"You always put so much into your show, every time you perform I can see that you really want it badly ," she said.
You always put so much into your show.
Sharon Osbourne to Sam Callahan
Opening the live show was music legend Nile Rodgers and Disco group Chic who performed classics such as 'Le Freak', which was followed by Luke Friend's rendition of 'Play That Funky Music' by Wild Cherry.
The Judges were impressed by the young singer with Sharon crowning him the "dark horse" of the competition.
Kingsland Road performed The Jackson 5's 'Blame It On The Boogie', while Tamera Foster gave an "elegant" rendition of Rose Royce's 'Wishing On A Star'.
Rough Copy received high praise for their performance of Earth, Wind and Fire's September, while the Judges declared Abi Alton back on top form following her own version of Gloria Gaynor's 'I Will Survive'.
Nicolas McDonald, 16, continued to receive positive feedback from the Judges as he took on Michael Jackson's 'Rock With You', while fan favourite Sam Bailey closed the programme with a show stopping performance of the Barbra Streisand and Donna Summer duet 'No More Tears'.
The former prison guard earned a standing ovation from all four Judges, with Nicole telling her "you were on fire".
"That was the vocal performance of the night by a mile," said Louis.
Gary added: "As the big ballad singer of the competition I was sure tonight you were going to struggle, how wrong was I?
"What a performance that was, it was flawless vocals."
The X Factor results show is on UTV on Sunday from 8pm.