The music mogul paired up teenagers Aaliyah and Acacia K to make a new act after they originally auditioned as solo acts.
14-year-old Student Aaliyah was first onto the stage full of confidence and energy. The singer and dancer is younger than Simon's jeans and vowed to show him and the other judges what she's got, singing AWOLNATION's Sail.
However she is asked to return with another track after Simon said: "I don't think you've come with the right song. You're better than those songs."
Next on to the stage was 15-year-old Acacia K, a student from Leyland, Manchester who promised to "smash it". Acacia sang Nicki Minaj and Skylar Grey's Bed of Lies for the judges.
Like Aaliyah, Acacia K was told her song choice wasn't right prompting Simon to suggest: "Can I have a word backstage?"
Behind the scenes, Simon paired up the girls and invited them to return together.
The duo later made a comeback with a cover of Bang Bang by Nicki Minaj, Ariana Grande and Jessie J.
"Was it perfect? No, but you only had an hour," Simon reacted. "What it was was fun, you had a sense of chemistry, I absolutely love you two."
Louis Tomlinson encouraged: "Musically, it's very different but that really reminded me of the first time in One Direction we performed on this show.
"There was just a magic in the air and the chemistry between you two.
"When other groups come on here we say to them, bring that chemistry that you girls have just brought. It's unbelievable, well done."
Robbie Williams added: "You've got to be family, you've got to love one another and see each other through thick and thin because you're going to need each other."
The X Factor 2018 continues Saturday and Sunday nights on ITV>