Ex-MMA fighter Javier Baez didn't just body slam a crazed knife-wielding assailant; he also "choked him out" ... telling TMZ his 15 years of pro training finally came in handy in the streets.

As we reported, the shocking clip making the rounds online shows Javier's attacker, Omar Marrero, didn't stand a fighting chance when he charged ... even though he had a 14-inch knife in his hand.

Javier tells us it all started while he was minding his biz, sitting in his car and talking to his fiancee -- he says that's when Marrero banged on his car window, shattering it.

He told Marrero to beat it, and warned he was going to call the police, but Omar brandished the giant knife -- and while some people would've driven off at that point, Javier stepped out of his car and the fight was on!

As you've seen, Javier body slammed Marrero to the ground, but what's harder to see is that he also blocked the knife by applying a chokehold ... which made the assailant pass out.

He then called the cops, and Marrero woke up with Javier's foot on his back.

With his amazing piece of ass-kicking going viral, Javier says he's getting a slew of calls from folks who want to hire him for personal and self-defense training.