Ex-UFC Fighter Melvin Guillard Knocks Dude Out Cold in Bar Brawl ... Wanted By Cops

9/7/2018 12:50 AM PDT

EXCLUSIVE

Ex-UFC fighter Melvin Guillard[1] -- who fought the likes of Nate Diaz[2] and Justin Gaethje[3] -- brutally attacked and KO'd a man in a Colorado bar ... and now cops are on the hunt. 

TMZ Sports has obtained surveillance footage which shows the 35-year-old getting into it with several people at Bar Standard in Denver around 2 AM on Monday morning. 

After some pushing and shoving, you can see Guillard -- with his trademark bleach blonde hair -- cold-cock a bar patron in the face ... knocking the guy out cold before he hit the floor. 

The victim was clearly unconscious and people ran to tend to him -- while a female patron tried to attack Guillard in retaliation. Guillard hit her too.

imageTMZ Sports spoke with a Denver Police Dept. spokesperson who told us several witnesses were able to identify the attacker as Guillard ... and now a warrant has been issued for his arrest. 

Guillard was a pretty promising MMA fighter when he first started out -- appearing on "The Ultimate Fighter" season 2. He famously scored a victory against UFC stud Jeremy Stephens[4] back in 2010. 

But, he also got his ass kicked a lot ... chalking up Ls to guys like Nate Diaz, Israel Adesanya[5], Justin Gaethje, Michael Johnson[6] and Donald Cerrone

We've reached to Guillard for comment -- so far, no word back. 

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