BOSTON — Realistically, the Boston Celtics were destined to clinch the NBA’s best record eventually regardless of their outcome Wednesday night. With six more regular-season games to follow their matchup with the Oklahoma City Thunder, the Celtics would have had plenty additional chances to wrap up the milestone, which provides a team home-court advantage throughout the playoffs. A loss to the Thunder only would have postponed the inevitable.

The Celtics just didn’t want a delay. Before rolling the Thunder 135-100, Joe Mazzulla challenged his team to capitalize on its first opportunity to clinch. Why? Because the extra pressure of such an experience could matter sometime down the road.

“We definitely talked about it as a team,” Mazzulla said. “Talked about it before the game. Trying to treat this game as like the clincher to kind of put that on ourselves to do that. I think it was important for us to simulate that.”

The Celtics, who clinched the top seed in the Eastern Conference on March 25, need to create their own motivation these days.

“Tonight was a night where it was like, if we win this game, we could achieve something,” Kristaps Porziņģis said. “Joe just kind of poked us a little bit and got us going for the game, knowing that we could clinch it, and we went out there and took care of business.”

After allowing the Thunder to pull close early in the second half, the Celtics dominated the rest of the way. Al Horford said Payton Pritchard’s energy late in the third quarter changed the momentum of the game. By the time the fourth quarter arrived, Horford said, the Boston players were “all locked in and trying to put the team away.” The Celtics opened the fourth quarter on a 12-4 run to extend the lead to 105-87. After a timeout called by the Thunder, who were without Shai Gilgeous-Alexander and Jalen Williams, the Boston players urged each other to keep piling on, Horford said.

“We made them call a timeout and then at that point, we were like, we have to take it to another level,” Horford said. “So for those next three, four minutes, we were able to win those minutes, and I think that’s what separated us. It was the mindset.”

The mindset the Celtics have tried to foster all season long.

“We want to feel like, in those moments, when we turn it up, we want to feel invincible — like nobody can mess with us,” Porziņģis said. “And we have that level that we can go to. And we did it today again. And I think that’s something that Joe has done a good job of developing for us and kind of putting that in our minds and in our toolboxes. And then opening it when we need it.”

The Thunder actually scored the first basket after their initial fourth-quarter timeout, but the Celtics scored the next 13 points. They struck one mighty punch after another on both ends of the court. Porziņģis slapped a one-handed touch pass to Derrick White for an open 3-pointer. Jaylen Brown drilled a long pull-up jump shot over Josh Giddey. White found Porziņģis for an alley-oop dunk. After another White 3-pointer, Brown rose up as if he were planning to shoot before firing a lovely pass to Jrue Holiday for a layup. Holiday’s bucket convinced Thunder coach Mark Daigneault to call yet another timeout.

“To start the fourth, I thought it was key for us to come out and not play games,” Horford said, “and really take it to another level.”

The Celtics controlled the fourth quarter so completely that Jayson Tatum, who finished with 24 points, stayed on the bench for the entire period. By the time he would have typically returned to the game, his team had already slammed the door shut on the Thunder. Boston outscored Oklahoma City 42-17 in the quarter.

Long before that, the bench jolted the Celtics awake twice. Near the end of the first quarter, Pritchard’s full-court pressure defense took precious time off the shot clock. It was meant to destroy some of the Thunder rhythm, but, for the Celtics, the benefits extended far beyond that. An old NBA saying suggests the first home game after a long road trip is typically one of the toughest on the schedule. The Celtics could have staggered through the entire night without their usual spark. Pritchard and the bench would not allow it.

Pritchard shuffled his feet to the right, then to the left. Back and forth, he stayed in front of the Thunder ballhandler. The Celtics’ second unit checked into the game with a burst. With a purpose. With an intensity. They would not leave the volume on low. As soon as Pritchard and Horford stepped onto the court, they turned everything up.

The starters still put in work. Porziņģis dominated the Thunder down low on both ends of the court en route to 27 points on 9-for-12 shooting. Brown broke out of what he called a “s— game” to score 15 points in the fourth quarter. But, in both halves, the bench lit the Celtics’ match. The second unit did its part to help the team reach the 60-win mark for the first time since the 2008-09 season.

“It was just we didn’t want to extend anything,” Horford said. “We wanted to come out and really lock in and handle our business and the mindset. Initially, I don’t think it was great. As the game went on, it got a little better. We made a run in the third and then really, end of the third, fourth, we kind of were able to impose our will. Just happy that we were able to get it done.”

The Celtics have bigger goals to accomplish. Even while finding ways to stay dialed in on the present, they have already shifted some of their focus to the playoffs. In another example of that, Brown said his slow start, perhaps related to a lingering hand issue (he called it “a sprain or like a strain on a ligament in my hand”), provided an opportunity to lean on the mental fortitude he will need during the postseason.

“I think just preparing your mind for the challenges to come,” Brown said. “You might be in a playoff game where you’re not feeling well. You’re banged up, your hand hurts, your back hurts or whatever the case may be, and nobody around here wants to hear no excuses. So tonight was a good opportunity to kind of prepare for some of those moments. Things aren’t going your way, stay locked in and it may change at any given point.”

Brown called it an honor and a blessing to be on a 60-win team, but he knows every team will be 0-0 as soon as the playoffs arrive.

“It’s a lot of hard work that went into that,” Brown said, “especially after coming up short last season, responding and coming back and not skipping any steps. So I think we’re on track, 60 wins, but when the playoffs start it’s back to square one.”