Video released by cops shows a man following a Bronx resident into his apartment building, where he sucker-punches him and knocks him out cold before making off with his belongings.

The thug followed the 63-year-old man into his Fordham Heights home near 182nd Street and Grand Concourse about 8 p.m. Friday, appearing to be talking on a cellphone, according to the surveillance footage.

The video later cuts to the man rushing his victim from behind and punching him in the head from behind, sending him falling to the ground.

The crook then rummages through the unconscious man’s pockets and takes $40 in cash before dropping his unwanted belongings and heading for the door, police said.

The brute — wearing a gray sweatsuit and a baseball cap — is seen from a different camera angle walking toward the front door, but stopping short of walking out.

He returns to the downed man and appears to take from him a white plastic bag before finally leaving the building.

The victim was taken to a hospital with a concussion and a swollen eye, police said.

Police are still looking for his attacker, whom they described as being about 250 pounds and 5-foot-9.