Police arrested a knife-wielding father for assaulting his girlfriend and holding the blade to his baby’s neck in Parkchester yesterday.

Russel Rivera, 30, was arguing with his girlfriend just before 3 p.m. on Archer Street near White Plains Rd when he snapped. The enraged man grabbed his baby boy and a knife and ran off, police said.

He later put down the knife and baby, who was unharmed during the chaos, sources said. The fight with his girlfriend turned physical.

Rivera was arrested and charged with assault, criminal possession of a weapon and endangering the welfare of a child.