It wasn’t a case of sink or swim.

A 33-year-old man escaped serious injury Saturday afternoon when the ground opened up on a Bronx sidewalk, causing him to plunge 15 feet, police said.

The victim, whose name was not released by police, suffered minor lacerations to his head after being virtually swallowed up, an NYPD spokeswoman said.

Firefighters responded to 4521 Third Ave. in the Belmont section shortly after 12:20 p.m. and pulled the injured individual out of the hole, FDNY officials said.

The man, who hit his head, was treated at the scene and taken across the street to St. Barnabas Hospital, officials said.

There was no immediate word on what caused the ground to suddenly open.