FISTS OF FURY DEPT.: In a moment of sheer terror during filming of her as-yet-untitled crime flick, JENNIFER ANISTON suddenly got knocked to the ground by an accidental wild punch that left her dazed and suffering!

As cameras rolled during an action scene, Jen – who plays the kidnapped wife of a millionaire – was feverishly swinging her designer handbag to break up a fight between two men who’d abducted her, played by JOHN HAWKES and rapper MOS DEF.

But Beauty got a bit too close to the action, and – as one actor swung at the other – POW!

A wayward punch slammed Jen’s jaw and she hit the deck hard! Badly shaken but conscious, she was helped to her dressing room and told the scene would be scrapped for that day.

But an hour later, Jen bravely insisted on returning to the set.

Hawkes and Def started apologizing profusely, but she just grinned and admitted: “Hey, I’m the one who messed up, not you guys!” And after slapping on new war paint for the reshoot, our hot li’l trouper nimbly ducked the boyz’ flying fists.