UFC commentators Joe Rogan and Daniel Cormier had just spent the past 30 seconds talking about Edwards appearing to accept defeat when he launched.
A left hand from Edwards caught Usman's attention and saw him drop his hands, leaving his head exposed as the left kick came crashing in.
"The greatest head kick knockout in the history of the sport," Rogan said.
The win for Edwards makes him the first Jamaican-born UFC champion and extends his winning streak to 11 fights.
It also snaps Usman's win streak and will see him fall from being ranked as the UFC's best pound for pound fighter.
Usman was taken down in the first round for the first time in his UFC career, but bounced back to control the fight over the next four rounds.
He had victory within his grasp, but Edwards refused to die wondering and his kick changed everything and sent fans watching on into meltdown.
"Oh my goodness," Cormier said.
"The way he pulled that out of the fire. He actually pulled victory from the jaws of defeat. I'm stunned. Leon Edwards just shook the world."
- with news.com.au
