The Boston Celtics beat the Dallas Mavericks 4-1 in the NBA Finals to win their first championship since 2008.

Jayson Tatum recorded 31 points and 11 assists as the Boston Celtics locked up their league-record 18th championship with a 106-88 blowout of the Dallas Mavericks in Game 5 of the NBA Finals.

Tatum also had eight rebounds while Jaylen Brown added 21 points, eight boards and six assists for Boston, which celebrated the 16th anniversary of its most recent title by completing a 16-3 playoff run.

The Celtics knocked off the Los Angeles Lakers in the 2008 Finals, and those two teams shared the league record with 17 championships apiece before Monday’s result.

Jrue Holiday had 15 points and 11 rebounds and Derrick White chipped in 14 points as Boston wrapped up the best-of-seven series on its second opportunity.

Brown was selected as the Finals MVP (most valuable player) after averaging 20.8 points, 5.4 rebounds and five assists.

Luka Doncic paced the Mavericks with 28 points and 12 boards, but he committed seven turnovers. Kyrie Irving finished with 15 points and nine assists for Dallas, and Josh Green netted 14 points.

After Dallas called a timeout with 3:11 left in the second quarter, trailing by 11 points, Boston completely broke the game open.

The Celtics scored 17 of the next 24 points, six of which came from Brown. Payton Pritchard capped the outburst in jaw-dropping fashion, canning a 49-foot heave from half-court at the buzzer to send Boston into the break with a 67-46 cushion.

Holiday’s layup pushed the Celtics’ lead to 78-52 with 9:10 to go in the third quarter. Green then converted a putback and knocked down a 3-pointer as part of a 10-2 run that got the Mavericks within 80-62.

Dallas later got the deficit down to 17, but Boston took an 86-67 lead into the fourth.

The Celtics were on top by at least 18 the rest of the way.

A three-point play from Tatum put the Celtics up 46-31 with 7:08 remaining in the first half, but Dallas then took over down low. The Mavericks scored all of their points in the paint during an 8-2 spurt to get within nine before Al Horford stemmed the tide with a hard-nosed layup.

Horford’s bucket came just before the Mavericks’ timeout that preceded Boston’s game-changing run.

Boston came to life in the final 1:39 of the first quarter, ripping off nine unanswered points to take a 28-18 lead into the second.

The Celtics wound up shooting 42.7 percent from the floor. Dallas shot 44.9 percent overall but was outscored by 10 points at the foul line and committed 13 turnovers to Boston’s nine.

It was Boston’s first NBA championship in 16 years.