Ultimately, for the Celtics to win this game against the feisty Nets, they were going to have to match Brooklyn’s grit and intensity. The pretty three-fluid basketball completely malfunctioned Friday night at TD Garden.

Because those shots weren’t falling, the Celtics had to adapt. They had to become the toughest team to play; they had to match Brooklyn’s intensity because the Nets played without fear, they played like a well-coached team and barely intimidated by the reigning world champions.

The Celtics are going to have to get used to this, inferior teams playing above their pay grade, challenging them defensively, chasing every rebound and loose ball, striking first and hoping to push the game into the final minutes.

This was the case when the Nets outplayed and dominated the Celtics for three quarters. Yet the Celtics withstood the charge, adapted mentally and schematically when those three slammed off the rim, and survived for a 108-104 overtime victory.

The lackadaisical play started right at the end, as the Celtics fell behind 12-0 and 16-2. It was going to be difficult, but what this club has learned from past bad defeats is how to respond to adversity.

The Celtics were 14 for 53 from the 3-point line. Sam Hauser, a career 41.8 percent 3-point shooter, missed nine of his first 10 attempts and many of them were wide open. Still, Jayson Tatum kept his faith, feeding Hauser in the right corner for a go-ahead three with 2:06 left in regulation.

Maintaining that faith and matching the Nets’ intensity is what secured the game. It’s good to have victories. It’s an 82-game season. The Celtics are not going to cruise every night. The goal is to be open-minded and versatile enough to play your best when not at your best.

“I don’t think guys make the decision to say, ‘We’re going to let them outplay us,'” Mazzulla said. “Sometimes you just have to give guys some perspective. Sometimes we play well and things don’t go as usual. The other team has a great coach and great players as well.

“I just thought we made enough plays to fix it. It’s a testament 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 will need full health to be as dominant as they want to be. Jaylen Brown missed his fourth straight game with a tight left hip flexor while Luke Kornet sat with hamstring pain. And for the second consecutive match, they were taken by surprise by the opposing intensity. They stumbled into this play looking completely disinterested and the sold-out crowd followed suit.

“It’s not an excuse at all but a perspective, one of the reasons we were good last year is because those are the kind of games we win,” Mazzulla said. “When you lose three rotation players (including Kristaps Porzingis), you have to find ways to win. Nobody cares, we have guys outside. It doesn’t matter and everyone in the locker room needs to know that we expect to win no matter who is on the field. If (the expletive) doesn’t work for you, you just have to understand it. I like their mentality. We had about 18 (types of matches) last year and that was one of them tonight.

Changing the mentality to become the team that plays the hardest in the middle of the game is difficult. The game rewarded the Nets in the first three quarters because they wanted to win the game more. They beat the Celtics on the boards and received big shots from scorer Cam Thomas while former Celtic Dennis Schroder sliced ​​into the paint for layups.

The Celtics looked bad in the first half Wednesday against the Warriors and even a 72-point second half couldn’t produce the victory. This time, they won the game thanks to their defense and timely shooting, including an Al Horford three-pointer in overtime that gave Boston the lead for good.

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

“(Mazzulla) always says it’s not going to go the way we hope,” 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 that you should expect it to happen unexpectedly. How will we react? How are we going to find a way to win?

“It’s not walking away from things that makes us who we are. We must always play the way we think, it’s the right way to play.

Hence the 53 3-point attempts on a night where the Celtics, besides Tatum and Payton Pritchard, were 6 of 33. The Celtics will always be themselves. They will never deviate from the plan, but what they have done in the Mazzulla era is create ways to win while they are not near their best. And it’s a handy skill to have.

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