A man wearing a medical face mask was caught on camera sucker-punching an NYPD officer in the Bronx Tuesday night as the cop’s partner was subduing a robbery suspect.

Nelson Jimenez, 31, launched his attack in front of a crowd of bystanders who had gathered on a sidewalk near 183rd Street and Davidson Avenue in University Heights to watch the arrest of 27-year-old robbery suspect Yoemdy Castro, law enforcement sources said.

One cop in the video can be seen holding Castro to the ground, while another stands nearby.

During the episode, Jimenez walks behind the standing officer, then socks him in the head, knocking off his winter cap, the video shows.

The officer who was struck immediately turns around and fires his Taser, but it’s unclear if it struck Jimenez.

Jimenez then runs away, with the cop close behind, the video shows.

Spectators can be heard cheering on the suspect, imploring the suspect to “run.”

Officers later caught and arrested Jimenez in a nearby bodega, law enforcement sources said. Charges against him are pending.

A second cop who responded to the fracas was also punched in the head in an off-camera incident, according to sources.

The suspect in that assault, Brandee Isom, 25, was arrested and charged with assault and obstructing governmental administration, sources said.