BOSTON (AP) — Jayson Tatum put his hands behind his head, with TD Garden fans standing on their feet cheering around him, and took it all in.

Walking to the bench, he wrapped both arms around Celtics coach Joe Mazzulla.

The journey was complete.

The Boston Celtics again stand alone among NBA champions.

Tatum had 31 points, 11 assists and eight rebounds, and the Celtics topped the Dallas Mavericks 106-88 on Monday night to win the franchise’s 18th championship, breaking a tie with the Los Angeles Lakers for the most in league history.

Boston earned its latest title on the 16th anniversary of hoisting its last Larry O’Brien Trophy in 2008. It marks the 13th championship won this century by one of the city’s Big 4 professional sports franchises.

“It means the world,” Tatum said on stage after the team received the trophy from NBA Commissioner Adam Silver. “It’s been a long time. And damn I’m grateful.”

Jaylen Brown added 21 points, eight rebounds and six assists, and was voted the NBA Finals MVP.

“I share this with my brothers and my partner in crime Jayson Tatum,” Brown said after the 107th career playoff game he and Tatum have played together — the most for any duo before winning a title.

Jrue Holiday finished with 15 points and 11 rebounds. Center Kristaps Porzingis also provided an emotional lift, returning from a two-game absence because of a dislocated tendon in his left ankle to chip in five points in 17 minutes.

They helped the Celtics cap a postseason that saw them go 16-3 and finish with an 80-21 overall record. That .792 winning percentage ranks second in team history behind only the Celtics’ 1985-86 championship team that finished 82-18 (.820).

Mazzulla, in his second season, at age 35 also became the youngest coach since Bill Russell in 1969 to lead a team to a championship.

“You have very few chances in life to be great,” Mazzulla said.

Luka Doncic finished with 28 points and 12 rebounds for Dallas, which failed to extend the series after avoiding a sweep with a 38-point win in Game 4. The Mavericks had been 3-0 in Game 5s this postseason, with Doncic scoring at least 31 points in each of them. He said the chest, right knee and left ankle injuries he played through during the finals weren’t an excuse for Dallas struggling throughout the series.

“It doesn’t matter if I was hurt, how much was I hurt. I was out there,” he said. “I tried to play, but I didn’t do enough.”

Kyrie Irving finished with just 15 points on 5-of-16 shooting and has lost 13 of the last 14 meetings against the Celtics team he left in the summer of 2019 to join the Brooklyn Nets.

Irving thinks better things are ahead for the Mavs.

“I see an opportunity for us to really build our future in a positive manner, where this is almost like a regular thing for us and we’re competing for championships,” he said.

NBA teams are now 0-157 in postseason series after falling into a 3-0 deficit.

Mavs coach Jason Kidd believes Doncic and his team will grow from this NBA Finals experience.

“I think the first step is just to be in it. I think that’s a big thing,” he said. “Yes, we lost 4-1, but I thought the group fought against the Celtics and just, unfortunately, we just couldn’t make shots when we had to, or we turned the ball over and they took full advantage of that.”

Boston never trailed and led by as many as 26, feeding off the energy of the Garden crowd.

Dallas was within 16-15 early before the Celtics closed the first quarter on a 12-3 run that included eight combined points by Tatum and Brown.

The Celtics did it again in the second quarter when the Mavericks trimmed what had been a 15-point deficit to nine. Boston ended the period with a 19-7 spurt that was capped by a a half-court buzzer beater by Payton Pritchard – his second such shot of the series – to give Boston a 67-46 halftime lead.

Over the last two minutes of the first and second quarters, the Celtics outscored the Mavericks 22-4.

The Celtics never looked back.

Russell’s widow, Jeannine Russell, and his daughter Karen Russell were in TD Garden to salute the newest generation of Celtics champions.

They watched current Celtics stars Tatum and Brown earn their first rings. It was the trade that sent 2008 champions Kevin Garnett and Paul Pierce to Brooklyn in 2013 that netted Boston the draft picks it eventually used to select Brown and Tatum third overall in back-to-back drafts in 2016 and 2017.

The All-Stars came into their own this season, leading a Celtics team that was built around taking and making a high number of 3-pointers, and a defense that rated as the league’s best during the regular season.

The duo made it to at least the Eastern Conference finals as teammates four previous times.

They finally reached the finish line in their fifth deep playoff run together.

After both struggling at times offensively in the series, Tatum and Brown hit a groove in Game 5, combining for 31 points and 11 assists in the first half.

It helped bring out all the attributes that made Boston the NBA’s most formidable team this postseason – spreading teams out, sharing the ball, and causing havoc on defense. And even chipping a tooth, like Derrick White did after he was landed on by Dereck Lively II.

“I’ll lose all my teeth for a championship,” White said.

And it put a championship bow on a dizzying stretch for the Celtics, that saw them lose in the finals to the Golden State Warriors in 2022 and then fail to return last season after a Game 7 home loss to the Miami Heat in the conference finals.

Tatum vowed that night to erase the sting of those disappointments.

Standing in a sea of confetti Monday night he was reminded by his 6-year-old son, Deuce, of what he’d accomplished.

“He told me that I was the best in the world,” Tatum said. “I said, ‘You’re damn right I am.’”