Louis Walsh's two groups had to sing for their place in the show after they received the fewest amount of votes from the public. It was the first time a judge has had two acts in the bottom two this series.
Mentor Louis refused to choose which one of his acts he wanted to send home, leaving it to judges Gary Barlow and Nicole Scherzinger - who both rejected three-piece band District 3. Judge Tulisa Contostavlos' vote therefore did not count, though she said she would have voted to save them.
Louis did not take part in the vote, saying to host Dermot O'Leary: "Dermot, I'm not voting. I'm not sending any of these acts home."
District 3, who sang Bruno Mars' Just The Way You Are in a last ditch attempt to stay in the singing contest, were thought to be not quite as "mature" as Union J by Nicole.
Union J, who belted out a rendition of Adele's Set Fire To The Rain in the sing-off, were highly praised by the judges on Saturday night after performing a version of Coldplay's Fix You.
On realising their fate, District 3 expressed disappointment and sadness at the fact their X Factor journey had ended, saying: "You know, it's the most gutting feeling in the world."
When asked by host Dermot why he thought his two acts were in the bottom two this week, Walsh suggested it may have been the case the two boybands split the vote, but added District 3 have nothing to worry about. "There's nothing wrong at all. They just didn't get enough votes," he said.
The Irish judge said he hoped the group get a record deal and added that they were a great group to have in his category. "They are a dream to work with," he said.
Last year's winners Little Mix - the first group to win the X Factor- sang earlier in the show, giving an energetic performance of their new single DNA.The four piece took to the stage in futuristic military-style outfits and crop tops of gold and electric blue.
Following their turn on stage, the girls' former mentor Tulisa expressed how proud she is of them, saying: 'My little muffins are all grown up… This is why you won, you're professional. you're all on point and confident now."
The girls – Jade Thirlwall, Perrie Edwards, Jesy Nelson, and Leigh-Anne Pinnock – already have two number ones under their belts, Cannonball and Wings. DNA is their first single, and comes from their upcoming album of the same name.
They made X Factor history last year when they became the first group to win the competition, beating popular Liverpool lad Marcus Collins to the title.