Kamaru Usman Rages at After-Party Following KO Win at UFC 261 Fight

Kamaru Usman was ready to party his face off after practically knocking Jorge Masvidal's face into space during UFC 261 ... and he did that and then some at a post-fight rager.

The Nigerian mixed martial artist swung by Myth Night Club late Saturday night after beating the brakes off Masvidal at the nearby VyStar Veterans Memorial Arena in Jacksonville, FL ... and club-goers were definitely ready to embrace the welterweight champ.

Usman was dressed to impress as well ... rocking a clean suit and some shades. He was ready to boogie too -- the guy didn't shy away from the dance floor, or the DJ booth.

We're hearing Usman showed up near closing time ... when DeeJay Capone was still blasting music. After the normies were kicked out -- an after-party proceeded ... which is what you see here in the video of the event we obtained. Looks like a good time was had by all.

The man had every reason to celebrate ... this after knocking out Masvidal cold with a clean, hard punch to the jaw. The KO went down in the second round, about a minute or so in.

Masvidal was actually laughing at Usman seconds before he got his clock cleaned ... and the crowd was absolutely stunned at how it all unfolded.