A Harlem open-air drug market became one of the safest streets in the city a day after The Post revealed how rampant drug dealing and consumption made the location hell on earth.

On Monday morning, a reporter observed two uniformed cops from the 28th Precinct on continuous foot patrol up and down Lenox Avenue between West 111th and West 112th streets, as the dealers who were there the previous day slipped out of sight.

“Today, the news makes a difference. Everyone is now concerned about this. Before, no one knows,” said Samaruddin Azizi, 59, who manages the Wonder Fried Chicken and Pizza at 21 Lenox Ave., where drug dealers had set up a headquarters before The Post’s exposé.

“Now the community has no stress. Now everyone knows and the community problem is shared with the whole United States.”

Unfortunately, the police presence appears to be only a temporary fix. At 12:34 p.m., the two officers left and The Post witnessed two “hand to hand” drug sales, right where the cops had been moments before.

As soon as the officers came back, the dealers scattered.

When a Post reporter pointed them out to the cops, they said they “can’t do anything” “unless we witness the hand-off,” which is a policing issue that’s developed ever since the NYPD’s “stop and frisk” tactics were ruled unconstitutional following a 2013 federal lawsuit.

One officer told The Post they were called to an incident at a nearby fast-food restaurant, but dealers often make “fake calls” to lure police out of the area.

“I was on a patrol like this once a few nights ago,” the cop said. “We got a call that a woman was being dragged into a deli. I knew it was a fake call to get us out of there the minute it came over. When we arrived, the block was quiet. They do that.”

An employee at the nearby Mac Liquors said consistent police presence is needed.

“[It] definitely makes a difference when they’re here. Yesterday, they stayed ’til about 11:30 a.m. It goes back to the way it was as soon as they leave. I wish they would stay all day, at least until I leave,” the employee, who identified himself as Luis, said.

By 1 p.m., four more cops showed up. Two were on the sidewalk outside the chicken restaurant, stopping to talk to anyone who was lingering on the street too long. Another two were briefly inside a Lenox Avenue candy store and the other two were behind the Fine Fare Supermarket, where The Post had observed drug dealing and using.

One cop said that the entire precinct has only four squad cars devoted to use by officers headed for foot patrol, implying that resources to address the problem are strained. They said they planned to be there all day, unless they got called to another job.

By 3 p.m., all the cops were gone.