UFC's new welterweight champ, Kamaru Usman, just can't wait to get a piece of Colby Covington -- so much so, in fact, that they almost came to blows inside a casino.

The two MMA fighters faced off (again) Sunday at the Palm Casino Resort in Vegas -- just a day after Kamaru man-handled former welterweight champ Tyron Woodley ... and was announced to fight Colby next by UFC prez Dana White.

It's also less than 24 hours after Kamaru and Colby nearly got into it just after Saturday night's UFC event. As he was leaving the Octagon, Kamaru came straight at Colby ... who was sitting nearby in the crowd rockin' a MAGA hat and his belt.

They were broken up and escorted away, but this time around ... there weren't as many security guards on hand to keep them separated near the A.Y.C.E. buffet in the Palm. The scene is pretty tense, as there were women and children around.

Check out the clip -- it's hard to tell who the initial aggressor was, but it looks like Kamaru's camp, including UFC manager Ali Abdelaziz, really tries to go in and attack Colby -- who circles back to get closer to Kamaru as punches are thrown by Ali ... but don't really connect.

Later in the video, you hear Colby tell someone on the phone that he just got swung on by Ali.

Eyewitnesses tell us more security showed up just in time before things got really out of control, and both men were escorted out of the building. We're told cops weren't called for this altercation.