Boogie Wonderland for 5 After Midnight while judges praise Honey G
The X Factor contestants took on disco classics with 5 After Midnight and Matt Terry impressing while the judges talked up novelty rapper Honey G.
A special performance from Sister Sledge opened the disco week episode with their classic hit We Are Family, before Saara Aalto kicked off the competition with her version of Donna Summer's No More Tears to praise from the judges.
But the most glittering comments were for trio 5 After Midnight, who took on an Earth, Wind & Fire mash-up of Boogie Wonderland and September with a dance break in the middle.
Judge Nicole Scherzinger told them: "I'm not even critiquing you when I'm watching you."
Simon Cowell added: "You have really popped the last couple of weeks...The best groups need a sense of humour and personality, and you've shown both."
They were followed on stage by Matt Terry with The Emotions' Best Of My Love which was also a hit with Cowell, Scherzinger, Sharon Osbourne and Louis Walsh.
Closing the show was controversial contestant Honey G, who offered a rap version of Bee Gees hit Stayin' Alive and as usual received glowing reviews after her performance.
Cowell told her: "I don't think I would have sang or rapped the Stayin' Alive part.
"This is where you are genius, it doesn't matter what the theme is, you give it 100%.
"I've never heard you complain or whinge."
Honey G, who admitted this week to having struggled with drug addiction, told the crowd: "I just want to go all the way to the final and win the show."
Also performing were Sam Lavery with Gloria Gaynor's I Will Survive, Ryan Lawrie singing Wild Cherry's Play That Funky Music, and Emily Middlemas performing Rose Royce's Wishing On A Star.
The X Factor continues on Sunday night on ITV at 8pm, when there will be no more life line vote and the bottom two contestants will automatically go into a sing-off where one of them will be voted out of the competition.