UFC's Polyana Viana Explains How She Destroyed Alleged Gun-Toting Thief

UFC badass Polyana "Iron Lady" Viana is telling TMZ Sports exactly how she disarmed and throttled a man who was allegedly trying to rob her at gunpoint ... and it's VIOLENT.

Dana White has already heaped praise on Viana -- a 26-year-old fighter with a 10-2 pro MMA record -- but now, she's giving us the blow-by-blow herself.

It all went on Saturday night when she was approached by a man outside of her Rio de Janeiro apartment. Viana claims he pulled out something claiming to be a gun and demanded her cell phone.

Worst. Mistake. Ever.

Polyana says she noticed the so-called gun "bent" when the guy touched it -- realized it was made of cardboard (not metal) ... and realized the only person who was in danger was the crook!!!.

"[I] thought, 'That's not a real gun.' So, I got up and threw 2 hooks."

"After that [I] just threw a kick to his face and that's the damage you all saw in the photos."

Polyana says those shots took the fight outta the alleged thief ... so then it was just about subduing the guy 'til cops arrived.

"He sat where he was and [I] grabbed him in a rear naked choke. He tried to hip escape a little bit. [I] was afraid he had a knife or anything that could hurt [me.] So, [I] didn't want to lose that position."

Authorities showed up, arrested the man and hauled him off to jail.

As for Viana, Dana White -- who's a helluva smart businessman -- booked her to fight a UFC 235 card in March.

#IronLady