It’s not often in sports when a long-term plan truly pays off.

Players get injured. Egos fray relationships. Shots simply don’t fall the way they’re supposed to.

For years, the Boston Celtics have been in the unenviable position of being labeled as “next up.” Even with the talents of Jayson Tatum and Jaylen Brown, two players with the privilege and burden of championship expectations for most of their careers, the stars never seemed to align for a ring.

A loss to the Golden State Warriors in the 2022 Finals was followed by last year’s disappointing defeat at the hands of the Miami Heat in the Eastern Conference finals. That’s when the pressure began to mount to get the job done.

Now, after taking down the Dallas Mavericks 106 to 88 in a decisive Game 5 of the NBA Finals Monday in Boston, the team has completed its long journey to the top. And for an NBA record 18th time, the Boston Celtics are world champions.

Three basketball players take up the center frame; two in green jerseys are behind a man with the ball in a white jersey.
Dallas Mavericks' Kyrie Irving, left, shoots against Boston Celtics' Jrue Holiday (4) and Jayson Tatum (0) during the second half of Game 5 of the NBA basketball finals, Monday, June 17, 2024, in Boston. (AP Photo/Michael Dwyer)
Michael Dwyer/AP AP

Afterwards, an elated and relieved Tatum described the last seven years as a roller coaster.

“To be able to say we did it, that we came together, and we won a championship. Banner number 18 has been hanging over our head for so many years. We won a championship,” he said.

The Celtics had a chance Friday to close things out in a sweep in Game 4 in Dallas after taking a 3-0 series lead, but bad shooting, worse rebounding and stellar performances from Luka Doncic, Kyrie Irving and the Mavs supporting cast sent the series back to Causeway Street.

But Monday night, 16 years to the day that the Celtics took down the Los Angeles Lakers to win their last championship in 2008, the Celtics took care of business.

Coming out of the gate, Boston was crisp on offense and stingy on defense. Tatum finished the first half with a near double-double. The Celtics held both Doncic and Irving to under 10 points and Payton Pritchard hit a walk off half-court three-pointer to send TD Garden to a frenzy as the Celtics led 67-46.

It was about as good of a start as you could ask for.

Dallas made it at least a little interesting after the break, but Boston’s big lead and hustle on the floor were too much to overcome.

A man in a green basketball jersey and green shorts holds his fists out to his sides and yells with a smile and his eyes closed. He stands on a green painted wood floor.
Boston Celtics' Jayson Tatum celebrates after scoring during the first half of Game 5 of the NBA basketball finals against the Dallas Mavericks, Monday, June 17, 2024, in Boston. (AP Photo/Michael Dwyer)
Michael Dwyer/AP AP

Instead of waiting for victory to come their way, the Celtics attacked rebounds and continued to make life difficult for Dallas on defense in the second-half. Their reward for their continued persistence was Boston’s most important win in nearly two decades.

Fans collectively roared when the final buzzer sounded, aware of the significance of an 18th banner.

Sisters Michaela and Alyssa Alperen and their mother, Lisa, of Peabody, were “ecstatic” after the game.

“We’re gonna celebrate with the parade, and then someone’s getting a Banner 18 tattoo,” Michaela said, nodding toward her mother.

Tatum finished with 31 points and 11 assists. Brown nabbed MVP honors, something he said he shared with his teammates. And after 17 seasons, Al Horford got his first championship. He recalled a meeting in 2016 when former team exec and Celtics legend Danny Ainge told him that “there’s nothing like winning in Boston.”

“And the fact that it has come, it has happened, JT, JB stepping up in a big way and leading us, it’s special,” he said.

When the Celtics lost to Golden State in 2022, it was clear the biggest piece they lacked wasn’t talent. It was the experience of a team that had been there before. This time around, they flipped the script, showing a less experienced Dallas squad why they had been the NBA’s best team this season. And that they learned the lessons of the past.

Now, after having nearly every title under their belt except the most important one before Monday night, these Celtics have etched a spot in history alongside the greats of this franchise’s past. And Boston can finally cash a check it’s been trying to take to the bank for a long, long time.

Elena Eberwein of GBH News contributed to this report.