The Boston Celtics had 16 years of cumulative playoff anxiety removed in one beautiful instant. For the first four games of the NBA Finals, the Celtics couldn’t dial in their three-point offense.

Open shots rimmed off; contested shots entirely missed the rim. But right before halftime of Monday’s Game 5 against the Dallas Mavericks, backup guard Payton Pritchard pulled up from behind midcourt and swished in a buzzer-beating heave.

Pritchard had made little effect in the series, save for a similar heave in Game 2. When Jesus stepped into his latest prayer, the TD Garden crowd rose in expectation and then screamed their approbation.

The Celtics, convinced now that the night and season belonged to them, stormed away from the Mavericks with a 106-88 victory to secure their record-setting 18th championship, breaking a tie with the Lakers, their major adversary.

The triumph is Boston’s first since 2008 following Finals losses in 2010 and 2022. Jaylen Brown was awarded Finals MVP, winning seven of the 11 media votes to edge out Jayson Tatum.

“I can’t even put into words the emotions,” Brown added. “I’m blessed and I’m grateful. My guys were great. They enabled me to lead us on both ends of ball, and we just came out and performed on our home floor.

[Finals MVP] might have gone to anybody. It could have gone to Jayson. I can’t talk enough about his selflessness and attitude. We did it collectively as a team, and that was the most essential thing.”

Boston’s clinching victory capped one of the most dominant seasons in recent years. The Celtics went 80-21 overall — 64-18 in the regular season and 16-3 in the playoffs — and won the Eastern Conference by 14 games over the No. 2 seed New York Knicks.

The Celtics’ breezy postseason run, which featured an Eastern Conference finals whitewash of the Indiana Pacers, was the shortest title chase since the Golden State Warriors went 16-1 in 2016-17. Their Game 4 blowout loss to the Mavericks on Friday was the Celtics’ only setback in their last 12 games.

To put away Luka Doncic and the Mavericks for good, the Celtics turned to their textbook winning recipe of balanced scoring and high-volume outside shooting and energetic defense.

Tatum shook off a poor start to take over in the fourth quarter, finishing with a game-high 31 points to go with 11 assists and eight rebounds. Brown contributed 21 points, and Jrue Holiday chipped in 15.

“These last seven years have been a roller coaster, up and down,” Tatum added. “I had to listen to all the s— that people said about me. Tonight, it was worth it. Oh, my God.

We came together and we won a title. Banner No. 18 has been hanging over our head for so many years. To know that we’re going to be engraved in history, it still hasn’t registered. I’m simply still trying to digest it all. But we did it.”

Doncic finished with a team-high 28 points — many of them coming after the Celtics were already up big — while Mavericks guard Kyrie Irving was held in check again, ending with 15 points on 5-for-16 shooting. Dallas had no viable backup plan with its star guards laboring early, shooting just 11 for 37 (29.7 percent) from deep.

“I’m sad we lost,” Doncic remarked. “I’m proud of every guy that stepped on the floor, all the coaches, all the people behind [the scenes]. Obviously, we didn’t win the Finals, but we did have a hell of a season.”

Pritchard’s backbreaking jumper was his only basket of the night, but it gave Boston a 67-46 halftime lead, spurred Brown to label his teammate a “f—ing legend” and inspired Celtics Coach Joe Mazzulla to call him “one of the best competitors and one of my favorite people in the world.”

The Celtics, who never trailed, stretched their lead to 26 points in the third quarter before cruising to a victory over a Mavericks club that simply couldn’t match their enthusiasm. Even yet, the TD Garden crowd spent much of the first half controlling its collective anxiety: Tatum, who missed his first four shots, drew huge, relieved shouts when he finished a drive through contact and thumped his chest with both fists midway through the second quarter.

After a quiet stretch to open the fourth quarter, Brown found a cutting Kristaps Porzingis, who returned after missing two games with an ankle ailment, for a thunderous dunk that brought the building to its feet.

Tatum and Brown both heard “M-V-P” chants as Boston put the closing touches on its victory. When Mavericks Coach Jason Kidd removed his starting in the closing minutes, Irving extended congratulatory hugs to Tatum and Brown, his old teammates on the Celtics, and Boston’s coaching staff.

Once Mazzulla emptied his bench with less than two minutes to go, Tatum held his head in shock before embracing Brown. Buckets of green confetti spilled from the rafters after the final bell, as Tatum lifted his baby son, Deuce, into the air to celebrate.

In a rowdy postgame locker room, Celtics owner Wyc Grousbeck smoked a cigar, members of the coaching staff sprayed champagne and the players took turns posing with the Larry O’Brien Trophy and a green championship belt. Written on the white board, behind a sign that read “Every possession matters,” were four words: “Noon flight to Miami.” The celebrations will continue in South Beach.

Despite their spectacular record and great finish, the Celtics were never fawned over quite like super teams of the past. There were some obvious explanations:

They lacked an all-time icon such as Michael Jordan, Shaquille O’Neal or Stephen Curry; they benefited from the postseason injury absences of Miami’s Jimmy Butler, Cleveland’s Donovan Mitchell and Indiana’s Tyrese Haliburton; and they spent much of this season trying to escape the shadow cast by their previous playoff disappointments.

Regardless of the competition, Boston returned as a better, deeper, more focused and more disciplined squad than the club that squandered a 2-1 lead in the 2022 Finals to the Warriors and fell into a 3-0 hole in the 2023 Eastern Conference finals against the Miami Heat.

Thanks to the offseason additions of Porzingis and Holiday, Celtics President Brad Stevens created the NBA’s best collection of talent and Mazzulla oversaw a complete team, packed with complete players, that started 11-2 and never looked back.

Boston ranked first on offense and second on defense in the regular season, then ranked fourth on offense and third on defense in the playoffs. Defying their lasting reputation for squandered leads and late-game follies, the Celtics went 21-12 in regular season games that were within five points in the final five minutes and 6-0 in similar games during the playoffs.

“Over the last couple years, we had some tough losses at home in the playoffs,” Tatum said. “We’ve lost the NBA championship at home in front of our fans.

We had a chance to beat Miami a couple years back and lost that one. To have the biggest win that you could have in front of your home audience — I felt like that was incredibly crucial to go out there and do all in my power to make sure we won this game.”

The tightly wound Mazzulla effectively pushed Tatum and Brown to take better care of the ball and to trust his offensive system, which focused primarily on catch-and-shoot three-pointers. Remarkably, eight different Celtics players made at least 100 three-pointers this season.

On defense, the Celtics’ versatility was their calling card; they used an aggressive, switching scheme to make life difficult for opposing perimeter talents such as Doncic and Irving.

Porzingis’s presence helped strengthen up their interior defense and rim protection while keeping the miles off 38-year-old center Al Horford, who won his first title in his 17th season.

“You can’t have a philosophy or a way of playing if you don’t have a group of guys that are willing to buy into it and be disciplined,” Mazzulla said.

“This group of guys has been through so much in the league. They know what it takes. It was a thrill watching the players simply grow as a team during the year but also really work at it. There’s a group of men in the locker room that decided they wanted to win on day one, and credit to them.”

Boston’s long-awaited title ultimately completed a narrative arc that began with then-Celtics president Danny Ainge’s 2013 blockbuster deal of Kevin Garnett and Paul Pierce to the Brooklyn Nets for a bundle of role players, future first-round picks and pick swaps.

By parting with two of the faces of its 2008 title team, Boston was able to obtain draft picks it utilized to acquire the two faces of this year’s title squad: Brown in 2016 and Tatum in 2017.

The full-circle moment was only attainable after some hard periods and innumerable reinventions. Boston hired Stevens from Butler University to head the rebuilding effort, and he won only 25 games in his first season.

The Celtics progressively ascended up the standings, but they cycled through endless players — Isaiah Thomas, Irving, Kemba Walker and Gordon Hayward, among them — as Tatum and Brown developed.

Brown described a 2017 vacation in Spain when he received a 4 a.m. phone call from Ainge.

“Don’t ask me why I was up,” he continued. “Danny asked me, ‘How do you feel about Jayson Tatum?’ I recall I played with him during the Top 100 camp.

He was my roommate at [Kevin Durant’s] top camp. We played on the same team in so many different [high school games]. At the Under Armour all-American game, we were roommates again. I had a lot of adventures with him. There was a lot of respect. I said, ‘I believe it’s a terrific choice.’ Fast forward from then, we’ve been winning ever since.”

As the big personalities around them came and went, a through line appeared for Tatum and Brown: Boston was good enough to make deep playoff runs but not great enough to win it all.

The Celtics reached the East finals in six of the prior eight seasons, but they progressed to the Finals just once before this year and crumpled on the championship stage against Curry, Draymond Green and Klay Thompson.

Hitting the wall repeatedly led to Ainge’s resignation and Stevens’s ascension from coach to president in 2021. When Stevens’s coaching successor, Ime Udoka, was sacked in 2023 following an unethical contact with a female co-worker, Boston turned to the 35-year-old Mazzulla, who was only a few years removed from coaching in the G League.

As the personnel changes and off-court turmoil developed around them, Tatum and Brown blossomed into all-NBA players and the Celtics rejected cries to break up their star wing combo.

In a series of clever transactions, Stevens acquired Horford, Derrick White, Porzingis and Holiday to assemble an experienced two-way team around his two-way star forwards and load up for revenge after a devastating season-ending defeat to the Heat last year in Game 7 of the East finals.

“We learned from all of our mistakes,” Brown added. “All of our adversity has made us stronger and tougher. All season you could see it. We made all the sacrifices.

We played both ends of the ball at a good level. We didn’t skip any steps. All the situations where we came up short, where we felt like we let the city down, let ourselves down, all of that compounded is how we arrive to this moment. The doubters may remain silent today, but they will be back next year with something to say.”

Sure enough, the Celtics turned those terrible experiences into eight months of beatdowns, removing any doubts that they were the league’s finest team this season.

“With the Celtics, everybody knows we only hang up championship banners [in the TD Garden rafters],” Tatum added. “It’s been a while since we’ve won one. … You [media] folks would probably think we didn’t play anybody to get here. So we’ll simply have to do it again next year.”