An NYPD cop took a shotgun blast to the face after being ambushed in Brooklyn by a suspected killer early Monday morning — but got off the fatal shot that downed the crazed gunman, police and sources said.

The deadly events began to unfold when Officer Sharjeel Waris, 25, was called to the scene of a homicide in Brownsville around 6 a.m., where a 41-year-old man was shot and left to die on the sidewalk.

Waris and a fellow cop were left to guard the crime scene — when things took a turn for the worse, NYPD Commissioner Jessica Tisch said.

At 7:45 a.m., the homicide suspect suddenly burst out of a first-floor apartment and fired a shotgun blast that hit Waris in the face — but not before the young cop got off at least one round that struck the killer. 

The brute barricaded himself in the apartment, holding police at bay until cops broke a first-floor window and flew a drone into the apartment.

That’s when they spotted the shooter “lying motionless on the kitchen floor with a shotgun on the floor near him,” Tisch said.

He was pronounced dead at the scene.

Investigators initially thought the gunman took his own life, but now believe the cop’s slug mortally wounded him, sources said. 

“We don’t believe there was a self-inflicted wound,” NYPD Chief of Detectives Joe Kenny told reporters Monday. “There was no ballistic evidence besides the shotgun lying on the floor.

“There were no discharged shell casings inside the apartment,” he said.

Cops have not identified the suspect pending further investigation, and have not revealed a possible motive for the earlier shooting, with the victim in that case identified by police as Leroy Wallace.

Waris suffered wounds to his face “consistent with birdshot pellets being fired from a shotgun” and was rushed to a Brookdale University Hospital.

He was released from the hospital in a wheelchair around noon as 100 uniformed police officers saluted and applauded him.

“Today’s another reminder of what’s at stake when your NYPD officers come to work,” Tisch said at the morning briefing. 

“They never know what’s on the other side of that door,” she said. “But whatever it is, they face it with an uncommon valor that defines this department.”

Waris, a four-year veteran of the force, took his test to become a cop when he was just 19 years old and received his badge at 21, according to Police Benevolent Association President Patrick Hendry. 

“He came within inches of losing his life,” the PBA chief said earlier in the day. “But because of his skill and his composure, he’s in that hospital room right now.”

In a bizarre twist, two other officers from the 73rd Precinct were in a car wreck while speeding to the initial call of at 1046 Thomas S. Boyland St.

NYPD brass said both officers and a motorist were all taken to Brookdale University Hospital with minor injuries after the crash.