"There was something in her voice," he relates. So he grabbed a broomstick which he later dropped for a metal bar, called 911 and ran downstairs "in my pajama bottoms - no shoes, no socks and no shirt," Ransone says.

He got to the vestibule in the nick of time. "There was this Hispanic guy in a blue sweatshirt choking my neighbor and pulling his [sex organ] out," he told Page Six's Lisa Marsh. "I pictured my mom, my girlfriend and every girl I've ever loved and thought, 'Vengeance is mine.' "

"I said, 'You rapist piece of [bleep]' and heard a crack when I hit his shoulder blade," Ransone says. "He mimed taking out a gun and said, 'Do you want to go to jail?' - and made a bee-line for the door.

"I cried, 'I'm not done with you yet' and kept swinging," Ransone says. Then the cops arrived and the attacker disappeared into the building. An arrest is expected soon.

"All of my friends would have done the same thing, but nobody else in my building came out," the actor says, adding, "I did what anybody would have done."