FBI agents stalked a New Jersey lawyer and suspected serial rapist in the “temptation room” of a popular Manhattan bar, collecting his DNA from a used fork to help crack the 16-year-old case, it was revealed in court Monday.

The five G-men secretly coordinated with the hot spot’s staff to keep tabs on Matthew Nilo — and by the end of the night had the crucial evidence they needed: the cutlery, four drinking glasses and a napkin, according to two agents’ testimony.

The agents took the stand in Boston court, where the 35-year-old suspect, accompanied by his fiancée, listened as his lawyers worked to try to get the DNA evidence tossed, grilling the witnesses for hours about how they gathered it, according to the Boston Globe.

The genetic material allegedly links Nilo — a lawyer who now lives in Weehawken — to the rapes of eight women in Charleston, Mass., and the North End of Boston in 2007 and 2008.

The cases had been cold until 2022, when investigators were able to take DNA from one of the victim’s rape kits and run it through popular commercial DNA websites to find possible relatives of the suspect.

Several of Nilo’s relatives were identified, and they agreed to have their DNA tested, narrowing the target down to Nilo.

The feds then launched their DNA collection after Nilo had been at the Oscar Wilde bar in Gotham on April 6, 2023, and he was arrested a few months later.

Nilo’s lawyers claimed in court Monday that the feds illegally collected the DNA without a warrant and also violated his privacy rights, since he was at a private work function at the time.

The suspect had been hanging out in a special section of the bar called the “temptation room” and featuring a marble fireplace and “the maximalist furnishings as is only true of the Victorian Era,” according to its website.

“I’ll call it stealing, you’ll call it abandoned,” defense lawyer Rosemary Scapicchio said of the collected DNA as she questioned one of the FBI special agents.

Prosecutors argued that the restaurant was a public environment and that Nilo gave up any rights when he let the dinnerware be taken away by restaurant staff.

Mark Bederow — a top New York-based defense lawyer who has cases in the Bay State but no ties to Nilo’s trial — told The Post he’s siding with prosecutors on this point.

“I don’t think an argument that they stole his DNA is going to work,” Bederow said.

The feds had a justified level of suspicion against Nilo because they had already conducted investigative genetic genealogy techniques using online genetic websites such MyHeritage.com and FamilyTreeDNA to narrow him down as the perpetrator, the legal eagle said.

And Nilo’s “property rights” to his dinnerware items were given up when the staff cleared them from the table.

“What happens when you’re done with the glass? They take it away,” Bederow said. “You don’t expect that you’re going to maintain control or possession of it.

“It’s abandoned property. … You’re not going to have a reasonable expectation of privacy.”

Bederow said many cases have been solved by such collecting of DNA evidence left behind by suspects — including Gilgo Beach killer Rex Heuermann, who was finally tracked down in the Long Island cold case after his DNA was retrieved from a pizza crust he chucked outside his Manhattan office.

“You’ve seen big cases crack this way. You did see it in the Long Island serial killer case where they found discarded pizza crust,” Bederow noted.

“That was perhaps more abandoned in the sense that he literally threw it away in the garbage, [but] it’s no different than, legally speaking, than a restaurant taking a glass, which you give up.”

The fact that the FBI dedicated all these resources to tracking Nilo down is “normal” especially given “they think he’s dangerous” Bederow added.

“He’s alleged to have been a serial rapist whose DNA has been linked to numerous attacks for which there was no identification,” Bederow said.

“So it’s not surprising that the FBI would use an all-hands-on-deck kind of technique to conduct an operation and then ultimately apprehend him shortly thereafter.”

The hearing over Nilo’s DNA is set to continue at a date in August.

Nilo, who has been out on $500,00 bail with GPS electronic monitoring, is facing charges of aggravated rape, rape, kidnapping and indecent assault and battery.

He’s pleaded not guilty.