Matt Cardle rocked out on The X Factor, winning a standing ovation from Cheryl Cole and Dannii Minogue.
Dressed in a simple white shirt and cream trousers, the Essex lad sat on a chair and played the guitar while singing The Moody Blues' record, prompting Cheryl and Dannii to get on their feet.
An impressed Louis told him: "It doesn't get any better than that... Brilliant song choice... emotional, heart-wrenching, note perfect."
Other rock night performances included Rebecca Ferguson's Motown-esque rendition of The Rolling Stones' Can't Get No Satisfaction and an upbeat version of Avril Lavigne's Girlfriend by Cher Lloyd.
As usual, the judges found reason to squabble, with Simon Cowell criticising Cheryl Cole for getting Katie Waisell to sing REM's Everybody Hurts.
He said: "The frustrating thing is that song does not work within that time period, it was chopped up like crazy. That song needs longer. I don't think you've given her the right opportunity at this stage in the opportunity."
Cheryl hit back, saying to Katie: "You filled your time absolutely beautifully and I believed every single word."
It also signalled a comeback - of sorts - for Wagner. He opened the show with Radiohead's Creep, after which even Dannii and Cheryl finally found kind words to say about him.
"I have to say that is the best you've sung in the whole competition and I think it's because you connected with the lyrics," Dannii said.
But they were less impressed with his version of Robert Palmer's Addicted To Love, with Dannii saying he was back to "the Wagner we know, the booing, the out-of-tune singing, the girls are back."