Celtics fans poured into Boston streets just seconds after Jayson Tatum and Jaylen Brown won the city an NBA title … and they celebrated in chaotic fashion — all while trashing Kyrie Irving in the process.

The impromptu block party began near TD Garden arena right after the C’s mercifully ended the Dallas Mavericks’ season by winning Game 5 of the NBA Finals, 106-88.

You can see thousands of green-clad fans flooded roadways — jumping on top of police vehicles … and chanting “F*** Kyrie!”

Some climbed onto light poles to shade the ex-Celtics star … before jumping off of them into swarms of people below. Others hung from street signs — and destroyed them in the process.

According to the Boston Police Department, a total of six adult men and two juvenile males were arrested in relation to the game.

The Celtics, meanwhile, celebrated their title in a bit more tame fashion. After they were drenched in confetti on the court — they hit up a nearby location for an after-party … where Tatum channeled his inner Kanye West to fire up a crowd.

“I know everybody would wonder what would happen if we didn’t win,” the Boston star said as he held the Larry O’Brien Trophy, “I guess we’ll never know!”

The team is reportedly headed to Miami for the next few nights to really soak in the championship … before they return back to Boston for a more traditional title parade.

Congrats!!!