A judge criminally charged with assault for drunkenly slugging a Legal Aid lawyer outside a Manhattan party insists the trash-talking defense attorney started the beef — and says he has the video to prove it.

Probation Judge Robert Beltrani, 54, was arrested for slugging lawyer Sam Roberts, 48, Oct. 20 and was suspended without pay pending the outcome of a disciplinary hearing.

The surveillance video, a copy of which was obtained by The Post, shows Roberts exit the Chelsea venue at 115 W. 18th St. and walk directly over to Beltrani as he chats with the party’s host, lawyer Andrew Bernstein.​​

After a 50-second conversation, Roberts clearly shoves Beltrani with his left hand before the feisty jurist nails him with a right cross to the face.

The dazed defender collapses to the concrete before Beltrani falls on top of him, gets up and walks away, according to the video.

“It was not a fight I wanted,” Beltrani told The Post.

“I’m 54 years old, I’m extremely overweight. It was after he hit me that I hit him,” said the administrative law judge for the Board of Parole.

Beltrani, a one-time Queens Republican state Senate candidate, said he was enraged by Roberts’ allegedly false narrative of the altercation to the press and prosecutors.

“He claims he didn’t provoke me, and that he was turning to walk away when I hit him,” the judge said. “It’s clear on the video that’s not true.”

The combatants were introduced for the first time earlier in the evening. Once outside, Beltrani, who had tossed back five vodka and sodas, says he told Roberts he’d be happy to help if he ever needed anything.

According to Beltrani, the lawyer sniffed, “‘You want to help people, help yourself, you’re a parole judge.’”

The incensed judge answered, “I have parolees who don’t speak to me the way you do. You should be more respectful.”

That’s when Roberts, who also admitted to having downed at least four vodka cocktails, shoved him, Beltrani said. “I had no intention of fighting that man and the video speaks to that,” he said.

“He hit me, I go backward against the wall — it was more of a reflex.”

Bernstein, whose law firm hosted the gathering, allegedly told prosecutors that before socking Roberts, Beltrani bellowed, “Yeah, I’m the judge. I do justice and I f—ing kill people!”

But Beltrani is adamant that he never uttered those words, and Roberts said in court papers he has no recollection of the judge making the menacing statement. Beltrani added that Roberts should have been charged for hitting him first and for perjury.

“If I had a parolee and he’s already convicted of a felony before me and I saw this evidence, I’m sending him home, not back to jail,” Beltrani said of himself.

Hit with misdemeanor assault, attempted assault and harassment raps, he previously rejected a plea deal that would have left him with no criminal record in six months, insisting he’s innocent and wants to take his case to trial.

“It’s a travesty this happened to me,” he said. “I’m a nice guy, I like to help people.”

Roberts, who suffered a black eye and separated shoulder, didn’t immediately return a request for comment. He admits in court papers that he had sarcastically told Beltrani, “Just remember, Judge, do justice. Do a little justice.”

After watching the surveillance video, Roberts conceded that he had touched the judge first and wasn’t turning away when the judge socked him but insisted he had no independent memory of this, according to court papers.

Beltrani’s defense lawyer, Dan Ollen, declined to comment.