After catching Borg in that EPIC flying armbar, the guys on the "TMZ Sports" TV show asked DJ if he cut Borg a break by not snapping the limb ... out of professional courtesy.

But if you thought DJ was being merciful, think again.

"No, no, no -- I was trying to break it the whole entire time," Johnson said ... "I'm breaking your arm if I get the chance."

DJ says Borg tapped right before he could get the arm in perfect fracture position.

The good news -- "I didn't hear any popping, so he should be fine."

Gotta watch the entire interview tonight on FS1 -- we also talked to DJ's wife about why she was "nervous as hell" going into the fight. It's great stuff.