11:04 AM PT -- 8/13 -- We just spoke with Williams about the encounter ... and, yeah, the fighter says the scene was as crazy as it looked on video!!!
Williams tells us the alleged thief was THIIISSSSSS close to getting away with his car ... but fortunately for the fighter, he says the guy just couldn't figure out how to work the parking brake.
As for cops, Williams tells us he never got them involved ... explaining he didn't believe there's anything further they could have done in the situation.
UFC fighter Jordan Williams whooped a dude's ass with violent knee strikes after he says the guy tried to steal his whip -- and the whole incident was caught on video.
The 30-year-old MMA star says it all went down on Wednesday ... when he claims a man tried to steal his ride right out of a convenience store parking lot.
Williams says the scene was captured on surveillance video ... claiming you can see in the footage a man got into his car while he was inside the store and then tried to drive off.
The video appears to show Williams confronting the guy before he got too far, though ... with the footage showing him ripping the man from the ride while kneeing him in the face.
In the clip, you see the man appears to run off while holding his head.
Williams says he could have made things even more violent ... writing on his social media page, "Wish I would of hit him with the trip after the clinch work when I tossed him out of the whip and finish off with some ground and pound."
"But," he added, "I'll settle with getting my car back."