A veteran NYPD detective just 10 days short of retirement was shot in the back in Brooklyn early Sunday after a gun-toting teen ran up to his unmarked police car and opened fire, cops and sources said.

Wounded Officer Robert Karroll, a married dad of three, was saved by his bulletproof vest, police said — while the 18-year-old gunman was nabbed a few blocks away during a dramatic foot chase.

The unidentified suspect had been caught on surveillance footage moments earlier oddly pacing back and forth on Nostrand Avenue near St. Johns Place in Crown Heights around 4:15 a.m.

He then racked a round in his .9mm’s chamber and ran up on the detective and three other cops who were inside a nearby unmarked black Kia SUV, according to police and video.

Investigators flock to where the shootout occurred in Brooklyn. Christopher Sadowski for NY Post Officers monitor the scene after the shooting. Christopher Sadowski for NY Post

Police are investigating whether the gunman knew cops were in the vehicle when he rushed it, sources told The Post. The officers were in uniform at the time.

Either way, the young nut sprayed their vehicle with gunfire, striking at least seven times, leaving bullet holes on the front and rear windshields as well as on the passenger side, police said.

The teen gunman shot up the unmarked NYPD vehicle early Sunday. Luiz C. Ribeiro for NY Post

Three officers returned fire, but the suspect was not struck, according to police.

Karroll was shot in the upper back while wearing his ballistic vest and miraculously suffered only minor injuries, police said.

The suspect fled on foot but was quickly nabbed several blocks away on Rogers Avenue and Union Street, police said.

After he resisted arrest and refused to be handcuffed, officers used a Taser to subdue him before taking him into custody.

It did not appear that the young gunman had been previously arrested in the Big Apple, although he’d been pinched for lesser crimes such as shoplifting in Essex County, NJ, law-enforcement sources said.

Karroll was taken to a local hospital for treatment and was expected to make a full recovery, police said.

He is fewer than two weeks from retirement, sources said.

“Today that vest saved his life,” NYPD Commissioner Jessica Tisch said at a press conference Sunday morning.

A second officer suffered bruises to her face and shoulder during the incident.

NYPD Commissioner Jessica Tisch, flanked by Mayor Zohran Mamdani and NYPD First Deputy Commissioner Tania Kinsella, speaks during a press conference Sunday. Luiz C. Ribeiro for NY Post

Surveillance footage obtained by The Post captured the bizarre moments that led up to the armed encounter.

The teen can be seen in the footage flashing his weapon as he restlessly walks back and forth on Nostrand Avenue about a half block down the street from the unmarked police vehicle.

At one point, he pulls back the slide of his pistol, then dashes up the block toward the parked police SUV and opens fire.

A picture of the alleged weapon used, a SAR 9mm handgun recovered from the scene, was shared by the NYPD on X.

An NYPD officer holds up a photograph of the firearm allegedly used in the shooting. Luiz C. Ribeiro for NY Post Police said detectives were fired upon as they got out of this unmarked car around 4:45 a.m. Sunday. Luiz C. Ribeiro for NY Post

The targeted officers had been reassigned to Brooklyn shortly after midnight as part of a stepped-up patrol for the NYPD’s July 4th violence reduction plan. They had been working the Sail4th 250 event in Lower Manhattan on Saturday.

Both of the wounded cops were with a sex-offender monitoring unit.

They were injured in violence that occurred nine years to the day that NYPD Officer Miosotis Familia was fatally shot by a nut career criminal while sitting in her patrol car in The Bronx.

There is no body-worn camera video of Sunday’s shooting because it happened quickly and unexpectedly, Tisch said.

NYPD investigators were going to local businesses Sunday to pull security footage to get a better sense of what happened in the run-up to the shooting, particularly as the suspect approached the vehicle, sources said.