If the Celtics ultimately wanted to pull away from this game against the feisty Nets, they had to match Brooklyn’s grit and intensity. The beautiful basketball with free-flowing threes was completely dysfunctional on Friday evening in TD Garden.

With those shots not falling, the Celtics had to adjust. They had to become the harder playing team; they had to match Brooklyn’s intensity because the Nets played without fear; they played like a well-coached team that was hardly deterred by the defending world champions.

The Celtics will have to get used to lesser teams playing above their pay grade, challenging them defensively, chasing every rebound and loose ball, hitting first and hoping to push the game into the final minutes.

Such was the case when the Nets defeated the Celtics through three quarters. Still, the Celtics withstood the onslaught, adjusting mentally and schematically as those threes clattered off the rim and survived for a 108-104 overtime victory.

The lax play started in the point, as the Celtics fell behind 12-0 and 16-2. This was going to be a grind, but what this club has learned from the bad losses of the past is how to respond to adversity.

The Celtics were 14 for 53 from the three-point line. Sam Hauser, a three-point shooter with a career percentage of 41.8 percent, missed nine of his first 10 attempts and many of them were wide open. Still, Jayson Tatum kept the faith and fed Hauser in the right corner for a lead of three with 2:06 left in regulation time.

Keeping that confidence and matching the Nets’ intensity is what secured the game. It’s okay to have victories. It’s an 82-game season. The Celtics don’t cruise every night. The goal is to be open-minded and versatile enough to play your hardest when you’re not at your best.

“I don’t think the guys are making the decision to say, ‘We’re going to let them beat us,’” Mazzulla said. “Sometimes you just have to give the guys perspective. Sometimes we play well and things just don’t go the way they normally do. The other team also has a great coach and great players.

“I just thought we made enough plays to kind of chip away at it. It’s a tribute to the team because you have to find ways to win ugly and that’s how it goes over the course of a long year.”

It has become clear that the Celtics need full health to be as consistently dominant as they want. Jaylen Brown missed his fourth straight game with a strained left hip flexor, while Luke Kornet was nursing hamstring soreness. And for the second game in a row, they were overwhelmed by the opponent’s intensity. They came into this game looking completely disinterested and the sold out crowd followed suit.

“It’s not an excuse at all, it’s a perspective. One of the reasons we were good last year is because these are the type of games we win,” Mazzulla said. “When you leave three rotation players (including Kristaps Porzingis), you have to find ways to win. No one cares that there are boys. It doesn’t matter and everyone in the locker room needs to know that we have the expectation to win no matter who is on the floor. If (expletives) don’t go your way, just figure it out. I like that mentality of theirs. Last year we had about 18 games like that and this was one of them tonight.”

Changing the mentality to become the harder-playing team in the middle of the game is difficult. The game rewarded the Nets through the first three quarters as they wanted to win the game more. They beat the Celtics on the boards and got big shots from scoring master Cam Thomas, while former Celtic Dennis Schroder cut into the paint for layups.

The Celtics looked bad in the first half against the Warriors on Wednesday and even a 72-point second half couldn’t produce a win. This time they won the game with defense and timely shooting, including an Al Horford 3-pointer in overtime that put Boston ahead for good.

Tatum led Boston with 33 points and added 9 rebounds, 6 assists and 2 steals. The Nets continually trapped him, pushed him out of his spot and forced him to make the right plays, like that corner pass to Hauser for the go-ahead lead in the fourth.

“(Mazzulla) always talks about how things won’t go the way we expect,” Tatum said. “The Nets are not the same team as last year. They play differently. They have a different coach (Jordi Fernandez). They play with more energy and freedom. (Mazzulla) always says it will be unexpected. How are we going to respond? How are we going to figure out a way to win?

“It’s not about distancing ourselves from the things that make us who we are. We still have to play the way we think is the right way to play.”

Hence the 53 three-point attempts on a night when the Celtics were 6 for 33 alongside Tatum and Payton Pritchard. The Celtics will always be themselves. They will never deviate from the plan, but what they have done in the Mazzulla era is figure out ways to win when they are not near their best. And that’s a useful skill to have.

Gary Washburn is a Globe columnist. He can be reached at [email protected]. Follow him @GwashburnGlobe.