Welcome to Celtics immortality, Payton Pritchard.

Despite playing the fewest minutes of any Boston regular in Monday’s NBA Finals clincher at TD Garden, the backup guard needed just a single shot to cement his status as, in the words of Finals MVP Jaylen Brown, “a (expletive) legend.”

After not seeing the floor for nearly the entire first half as head coach Joe Mazzulla tightened his rotation, Pritchard checked in four seconds before halftime and buried a miraculous buzzer-beater from beyond halfcourt.

His 43-foot heave gave the Celtics a 67-46 halftime lead, and the Mavericks never recovered. Boston cruised to a 106-88 win to secure their first NBA title since 2008.

“We had an excellent game plan in the Finals, and then all of the guys contributed,” Brown said postgame. “Like, for example, like Payton Pritchard — unreal, right? Unreal. Like, just comes in the game and drains one from halfcourt. That dude, he’s a (expletive) legend, man. Shoutout Payton Pritchard.”

Those four seconds were the only meaningful ones Pritchard — a core rotation player who played in every regular-season and playoff game — logged in Game 5. He did not reenter until there was 1:21 remaining in the fourth quarter, subbing in for Brown with the Boston up 20 and the celebration already underway.

Statistically, it was a rough Finals for Pritchard, who went 3-for-16 on 3-point attempts and totaled 17 points across the five games. But those numbers will be quickly forgotten. What Boston will remember were his two unlikely buzzer-beaters: one in Game 2 and the second Monday night, which came off a missed Luka Doncic free throw.

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“Man, that was beautiful. That was beautiful,” said Al Horford, who grabbed the rebound and fed a pass to Pritchard. “He did that, and you take a glance at the other team, and it’s one of those that breaks your spirit. And then it just kind of fueled us.

“But Payton, man, that just sums it up. It was ups and downs for him, not knowing what to expect, when to play, when not to play. He’s the kind of guy that he is a big-time player, and it’s hard because we have a lot of guys. But man, him stepping up, cold, ready, not afraid of the moment, taking the shot. And man, as soon as he shot it, I was like, ‘Man, he’s about to knock it down.’ Like, this is crazy. So, man, the fact that he knocked it down, like that was huge. That was special.”

One notable viewer felt differently. As Pritchard’s teammates mobbed him on the court, Kansas City Chiefs quarterback Patrick Mahomes — a Texas native and Mavericks fan — tweeted: “Bro I hate this dude.”

Mahomes surely was not the only Mavericks supporter who feared the worst when Pritchard released the ball. A week earlier, they watched the energetic 26-year-old bury a 34-footer as time expired in the third quarter of Game 2. In both games, those were the only shots Pritchard made.

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Mazzzulla, who raved about Pritchard’s unselfishness after Game 2, said he inserted him into Game 5 specifically to attempt a desperation heave.

“Payton is one of the best competitors and one of my favorite people in the world,” the coach said. “Just the way he competes, the professionalism and just for his ability to take pride in stuff like that. He’s really grown as a player this year to becoming a well-rounded player on both ends of the floor, and he won us games. I think he won us moments. …

“Those guys have to win moments of games for you, and Payton did that twice for us. That is just as important as any other plays that happened throughout the series and in the playoffs alone. I’ve got a huge heart for him.”

Now, Celtics fans do, too.