New York City’s first transit cop-turned-mayor joined a team of the NYPD’s finest to patrol the subways after dark — and took The Post along for the ride.

During more three hours underground, Mayor Eric Adams traveled across Manhattan and Brooklyn, observing the changes that have taken place since he worked the beat.

Amid this year’s surging crime rates — including an alarming, 54% spike in the transit system — Hizzoner compared his challenge to the one that faced former NYPD Police Commissioner Bill Bratton, whose “broken windows” strategy helped bring both the subways and the city under control during the 1990s.

“We can no longer ignore quality-of-life issues,” Adams said.

“I am again where Bratton was.”

In a chilling sign of the times, Adams had to delay the planned start of his trip so he could stop in Harlem to visit the parents of college basketball star Darius Lee, who was killed in a mass shooting at a neighborhood cookout just hours earlier.

Here’s what The Post saw late Monday and early Tuesday:

Adams arrives wearing an NYPD cap and a navy blue windbreaker with the words NYC MAYOR in yellow on the back and his name over his heart.

A top adviser, Tiffany Raspberry, swipes a MetroCard so her boss can pass through a turnstile, after which three people approach and ask to take photos with Adams, with one man overheard telling the mayor about his wife’s disability.

“You never know who you’re going to see on the subway,” Hizzoner says afterward.

NYPD Sgt. Victor Tavarez, leading a five-member Transit Bureau team, greets Adams and says that after boarding a train, two cops would patrol the front cars while two patrol the rear, and also look out the windows each time the train stops at a platform.

After getting on a No. 2 train, Adams compliments Tavares on his leadership skills and predicts that the 40-year-old will move up the ranks of the NYPD.

“These are the qualitative supervisors,” Adams later tells The Post.

“These cops are gonna do their job.”

Adams and the cops get off the train and walk through the station to the southbound N-Q-R-W platform where they board an R train.

Adams sits down next to a woman, “Melissa,” who shoots a selfie video with him.

Seated across the car are a mother and son from Virginia, with the mom telling Adams they’re on the teen’s “graduation trip” and staying at a hotel on 36th Street.

“You gotta come here to live, man,” the mayor said.’

“He wants to!” the woman said of her son, who’s wearing a Yankees cap.

After the tourists get off at the 34th Street-Herald Square station, Adams, a 62-year-old Brooklyn native, reminisces about riding subway trains during the crack epidemic of the 1980s.

“You know, this subway system was gloomy. It was gloomy,” he said.

“It was frightening just to be in the system, you know.”

Adams gets off the train and peers across the tracks at two women who are staring at their cellphones while standing apart in a poorly lit area between a staircase and the tracks.

“See now, look at this,” he says.

“They should not be there, these two young ladies, standing by themselves, out of sight, in this hidden area.”

Instead, Adams says, “They should be standing by, you know, the help button right there, right near the steps.”

“We have to be smarter riders to not allow people to be the victim,” he adds.

Adams says that when he was a transit cop on patrol, he was always on the lookout for potential victims — and freely admits having profiled people to do so.

He also foresees the women across the tracks setting themselves up for future trouble.

“This time of night, those ladies are standing by themselves,” he says.

“And then, that habit becomes: 1 in the morning, when they’re coming from the party, ‘I’ma do the same thing.'”

The next day, Adams seizes on the incident as he discusses subway safety at a news conference in Brooklyn.

“We’re going to move with the MTA to put in place a massive campaign on how to be a safe passenger,” he says.

“Many people don’t know the best place to stand during the late hours is in the conductor’s position. There are zebra stripes near the ceiling on a bar that tells you where the conductor position is. We need to educate people to do that.”

Following a short trip on a Brooklyn-bound N Train, Adams meets NYPD Lt. Ryan Murphy, who’s been assigned to the Transit Bureau since 2008.

Murphy tells the mayor that the night has been fairly quiet, with some subway riders playing loud music and a few visibly intoxicated.

“How’s the communication?” Adams asks, referring to the NYPD’s handheld, two-way radios.

When Murphy says they’re working fine, Adam recalls how when he was on the job, “you had too many dead spots in the system” and how cops had to tap their nightsticks to alert colleagues when their walkie-talkies weren’t functioning.

Murphy tells the mayor that there are “a lot of quality of life issues we’re trying to deal with currently, adding that riders who arrive in the station will often tip him off to unruly or emotionally disturbed passengers by clearing their throats and gesturing with their eyes.

“And now you know, it’s like, ‘Hey, I’m gonna come in and say hello to people in this train car maybe a little bit more thoroughly,” he says.

“We talk and, you know, we got to hold the train another minute. You know, people normally don’t like us because of that, but it’s just to make sure that we’re not letting any kind of issues go downstream. We can handle them while we can take care of everything right here.”

While patrolling the station with Murphy and the other cops, Adams is approached by Yemeni immigrant Saad Alansi, 29, who brings along a friend’s kids, ages 7 and 8, to pose for a photo with the mayor.

Alansi later tells The Post he initially feared that Adams’ presence meant there’d been another incident like the April 12 mass shooting in the 36th Street subway station in Sunset Park.

But when a cop told him that wasn’t the case, “I said: Are you serious? I am going to meet him now!”

During his conversation with Adams, Alansi says, “I said he is doing great job, especially in this time because America is down.”

“But we need strong people like Mr. Adams. He’s going to be No. 1 for New York,” he adds.

“We all Yemenese people work in smaller store and market. We need him to support us.”

Adams arrives at the end of the N line, where MTA employees are waiting on the platform with buckets of strong-smelling cleaning liquid.

Adams shakes hands with cleaners and walks up to a team of homeless outreach workers in orange T-shirts who were about to start their shifts.

One, Shukura Cooper, stands with a dazed and disheveled young man wearing a green-and-white striped shirt with a dark-colored stain — possibly blood — down the front.

Cooper introduces the homeless man to Adams, saying, “This is the mayor.”

“The mayor of what?” the man asks.

Amid laughter, Cooper says the man — who holds a pair of socks in one hand and has a change of clothing draped over a shoulder — has agreed to accept help from the city, including a bed in a shelter.

But when Adams walks away, the homeless man drifts off, with DHS Deputy Commissioner Cassandra White saying Wednesday, “He is someone who is clearly entrenched…he took clothing, she gave him socks. But he could not accept the services.”

About 15 minutes after the encounter, as Adams is preparing to leave the station, another homeless man approaches him, jangling a key ring and repeatedly shouting, “I got my keys!”

White tells Adams, “Sir, this is not scripted” and says the man was headed to a “safe haven” homeless shelter when he heard Adams was in the station and said, “I want to see the mayor!”

Adams visits his old stomping grounds in the subterranean headquarters of Transit District 34, where the mayor began his police career in 1984.

After walking behind the front desk to examine the log book, Adams seems wistful as he chats with the cops on duty.

Later, he says, “It’s almost deja vu to be back here in District 34, a place I started my policing career.”

Adams recalls “patrolling the subway, riding the trains, 8 at night to 6 a.m. in the morning, five days a week during a very dangerous period in our city.”

“But everything I learned is part of what’s being the mayor now, what I learned here in those early days of policing,” he says.

After ducking out of the station to buy a cup of tea with almond milk and two bags of peanuts, Adams says, “Y’all not ready to quit?” as he announces that he’s going to extend his tour and take the F train to the Jay Street-MetroTech station in Downtown Brooklyn.

The station is located just steps from Borough Hall, which Adams ran as Brooklyn borough president before being elected mayor.

The F train, he says, has a “different energy” because the cars are wider and have more space between the seats on either side.

While Adams waits to depart, a female MTA worker approaches to take a selfie with him.

“Let’s make your boo jealous,” Adams says and they both laugh.

Meanwhile, train operator James Rabel says he’s “riding shotgun” with the mayor and calls the early morning trip the “highlight of my career.”