An 81-year-old filmmaker known for horror cult classics like “Blood Sucking Freaks” was busted on New Year’s Day for attacking a woman in his building on the Upper West Side, authorities said.

Joel Reed, whose weirdo flicks include 1981’s “Night of the Zombies” and the 1975 “G.I. Executioner,” violently groped the victim in an apartment at 120 West 58th St., they said.

“She [the victim] observed the defendant place his hand on her groin over her clothing, twist her hand, push her to the ground, causing redness and swelling to her right finger, shoulder, hip, and susbtantial pain,” a criminal complaint states.

It’s unclear whether the incident occurred in his crib or another residence in the luxury building.

Cops arrested the feisty octogenarian at his pad at about 3 a.m. He was arraigned in Manhattan Criminal Court Thursday night and released without bail, court records show.

He faces misdemeanor raps for assault, forcible touching, sex abuse and harassment, the complaint states.