For the 18th time in franchise history, the Boston Celtics are NBA champions.

The Celtics closed the first quarter of Monday’s NBA Finals Game 5 on a 9-0 run and never looked back en route toThe win secured a 4-1 win in the NBA Finals and the franchise’s first title since 2008.

The Celtics set the tone from the opening tip as they took the floor for the first time in these Finals wearing their classic green uniforms. They proceeded to put on a performance worthy of those colors. It was also worthy of a team that rolled to an NBA-best 64 wins in the regular season and produced advanced metrics that

They did it on Monday with defense. They did it with 3s. They did it with stars Jayson Tatum and Jaylen Brown leading the way. It was an optimal conclusion to a seminal Celtics season.

Boston fired the first shot Monday, opening a 9-2 lead with its first three buckets scored by Jrue Holiday. Dallas punched back and closed the gap to 19-18 in the final two minutes of the quarter. But the 9-0 run to close the quarter pushed the Boston lead to 28-18.

The second quarter saw more of the same and ended with a buzzer-beating Payton Pritchard heave from beyond halfcourt to extend the Boston lead to 21 points.

Dallas never recovered.

There was no Celtics letdown after halftime. Boston extended its lead to as much as 26 points in the third quarter and never let Dallas again sniff striking distance. The fourth quarter was a coronation.

Tatum overcome with emotion, Brown wins MVP

After watching Brown, Holiday and Kristaps Porziņģis take headlining roles throughout the Finals, Tatum took the reins Monday night as a scorer and playmaker. He led the game with 31 points and 11 assists alongside eight rebounds and two steals. He turned the ball over just twice.

When it was done, he buried his face in his hands as confetti fell from the rafters, overwhelmed with emotion. He then celebrated with his son, Jayson Jr.

Brown added 21 points, eight rebounds, six assists and two steals. For the series, he averaged 20.8 points, 5.4 rebounds and five assists, an effort that He can add the trophy to his collection alongside his Eastern Conference finals MVP hardware and forever silence the critics of and his left hand.

Derrick White once again came up big on both sides of the floor with 14 points, eight rebounds, two steals and one block. He paced the Celtics from long distance on a 4-of-8 effort.

Holiday — now the missing piece that completed a championship run  — added 15 points, a team-high 11 rebounds and four assists.

As a team, the Celtics dominated the glass with a 51-35 rebounding edge. They forced 13 Mavericks turnovers while giving the ball away just seven times. Concluding a running theme throughout the series, Boston secured a significant edge at the free throw line with a 17-of-20 (85%) effort. Dallas struggled again while shooting 7-of-13 (53.8%).

The Celtics slowed down from 3 after halftime in a 13-of-39 (33.3%) overall effort. But they built their 21-point halftime edge while shooting 10-of-21 (47.6%) from beyond the arc.

Mavericks stars struggle again

A Mavericks team that staved off a sweep appeared to leave everything on the floor in Dallas. The Mavericks were outmatched and outplayed from the opening tip Monday night and provided little challenge to an overwhelming Celtics unit.

Luka Dončić led Dallas with 28 points, 12 rebounds, five assists and three steals. He struggled from 3 (2 of 9) and continued to provide little resistance on defense. He turned the ball over seven times.

Former Celtic Kyrie Irving — who appeared overwhelmed in Games 1 and 2 in Boston — struggled again Monday night on a 5-of-16 effort from the floor as he was repeatedly jeered by the home crowd. He finished with 15 points and nine assists.

What this title means for Celtics

For the Celtics, the championship alters legacies on multiple levels.

In the grand scheme, the Celtics reclaimed sole possession atop the list of all-time NBA champions, no longer tied with bitter rival the Los Angeles Lakers. The Lakers had previously won eight titles against Boston’s one since 1986, including three unanswered since 2008 to tie the Celtics with 17 titles. Boston stands alone once again with its 18th championship.

Tatum and Brown are now certified. The All-Star teammates were repeatedly questioned and criticized for coming up short on the biggest of stages in their previous six seasons as the shared faces of the franchise. They were flummoxed in two Eastern Conference finals by the Miami Heat and watched Stephen Curry and the Golden State Warriors celebrate a championship at TD Garden in 2022. Those questions linger no more.

Tatum and Brown now join a hallowed list featuring Kevin Garnett, Paul Pierce, Larry Bird, Robert Parish, Kevin McHale, Dennis Johnson, JoJo White, Dave Cowens, John Havlicek, Bob Cousy and Bill Russell in leading a franchise synonymous with greatness to championship glory.

President of basketball operations Brad Stevens took his unique basketball mind from the Celtics sideline to the front office in 2021. Never satisfied with coming up short, he continually tinkered with the roster and ultimately made championship-building moves, including acquiring Al Horford, Holiday, White and Porziņģis — decisions that coincided with difficult calls like parting with franchise favorite Marcus Smart and All-Star Kemba Walker.

Head coach Joe Mazzulla — promoted in 2022  drew fire throughout his first season leading the team that ended short of the NBA Finals. Now, he’s a champion in his second season as an NBA head coach.

For these Celtics, this championship isn’t viewed as an end, but a beginning. Tatum (26 years old) and Brown (27) are just reaching their primes and have their sights set on further cementing their names into Celtics franchise glory. But what a beginning this championship season was.