Scratch Edson Barboza from the ranks of the unbeaten.
Barboza got off to a strong start, looking to chop Varner down with leg kicks, but the fight shifted when Varner caught a kick and took him down, scoring ground strikes.
Barboza got back to his feet but Varner staggered him with a straight right hand. He dropped him with another right and dropped a series of hammerfists over his fallen opponent until ref Steve Mazzagatti had seen enough.
The former WEC champion immediately ran to a camera and mouthed the words, "I'm back."
"Once you hit rock bottom you appreciate the places you've been, so I just want to thank the UFC for another chance," he said.
Varner, who had taken the fight on short notice, improved to 19-6-1 with 2 no contests.
Barboza had come into the fight as more than a 5-to-1 favorite. He was 10-0 coming into the fight and had won three straight Fight of the Night awards. On this night, he might be on the wrong end of another award, Knockout of the Night, as Varner returned with a flourish.
It was his first time in a UFC cage since March 2007, a fight that also ended in a first-round stoppage victory.