BOSTON — How did the Boston Celtics close out the Dallas Mavericks in Game 5 of the NBA Finals?

The Celtics, who claimed their record 18th NBA title with Monday’s win, rode hot stretches and took advantage of key swings in momentum to win their first championship since 2008.

These were the five moments that sealed Game 5 for the Celtics:

Al Horford gets the party started

Al Horford forced the Mavericks into their first timeout when he drilled a 3-pointer from the top of the key to give the Celtics an early 9-2 lead with 7:26 left in the first quarter.

Prior to the shot, the early moments of the first quarter had been a bit of a grind for both teams. Jrue Holiday had scored the Celtics’ first six points — all in the paint. Horford’s long-range strike gave Boston its first fire from beyond the arc.

Horford, a 17-year veteran, is finally an NBA champion.

Celtics steal momentum as first quarter closes

The Celtics grabbed a heap of momentum at the end of the first quarter.

Leading 21-18 at the time, Sam Hauser drilled a 3-pointer and forced a turnover on the ensuing possession. That led to Jayson Tatum finding Finals MVP Jaylen Brown for an easy layup under the basket.

Dallas failed to score on the next possession and Tatum found the basket next for the Celtics, giving Boston a 10-point lead as play moved to the second quarter.

Derrick White leaves it all on the floor

The Celtics’ high-octane effort was on full display when Derrick White took a faceplant into the parquet to grab a loose ball. White dove alongside the Mavericks’ Dereck Lively which resulted in White’s head hitting the floor.

White chipped his front tooth and both his front teeth were loose after the impact, according to the ABC broadcast.

White stayed in the game and chipped in 14 points and eight rebounds.

Payton Pritchard does it again

Payton Pritchard drilled his second halfcourt buzzer-beater of the NBA Finals to give the Celtics a 67-46 lead at halftime. He also connected in Game 1.

Pritchard’s strike Monday felt like a backbreaker for the Mavericks, who had worked tirelessly to keep pace with the Celtics despite struggling to find an offensive rhythm. That shot made it a 21-point lead at the break (then the largest of the night) instead of 18, which felt like a much bigger margin for Dallas to overcome.

Pritchard is becoming something of a specialist with these, as coach Joe Mazzulla intentionally enters him into the game when the Celtics have an in-bound possession in the final seconds of a quarter. And why shouldn’t he?

Kristaps Porzingis makes presence known

It was unclear whether Porzingis, battling a rare leg injury, would dress for Game 5. But he did. And his impact was felt most when he slammed home a dunk with 9:08 left in the game to give the Celtics a 21-point lead.

To be fair, the game felt in hand for the Celtics at this point. But the crowd at TD Garden had been waiting for their beloved Porzingis to make a statement — and this was it.

Porzingis totaled five points in 13 minutes.