Joe Mazzulla knew the Thunder weren’t a pushover, and the Celtics needed a big rally to beat them

Shai Gilgeous-Alexander certainly didn't look fatigued in the second game of a back-to-back for Oklahoma City, pouring in 37 points despite the best efforts of Al Horford and Co.Jim Davis/Globe Staff

Before the Celtics faced the Thunder on Monday night, coach Joe Mazzulla thought it was important to do some myth busting. Yes, the Thunder have collected future first-round picks the way kids collect basketball cards of first-round picks. Yes, they’re young, and their brighter days are most likely somewhere down the road.

But that does not mean they will fall over once an opponent offers a good huff and puff. That does not mean that games such as this one will be easy.

“That’s what we tried to debunk before the game,” Mazzulla said. “That team is good. They’ve beaten good basketball teams, and they put pressure on good basketball teams for all 48 minutes.”

Maybe Mazzulla’s words did not sink in right away, because Oklahoma City controlled the better part of the first three quarters and roared to a 15-point lead.

But the alarm bells went off before it was too late, as Boston got a jolt from its bench, suffocated the Thunder’s ball-handlers, and received a powerful closing kick from Marcus Smart before securing a 126-122 win, its seventh in a row.

Jayson Tatum had 27 points and Jaylen Brown added 26 for the Celtics, but the two stars were far from perfect. Tatum was 1 for 9 from the 3-point line, and Brown was 0 for 5 and committed five turnovers.

This game was won elsewhere. With the starters sleepwalking through certain stretches, Mazzulla turned to Payton Pritchard and Derrick White to provide a burst of on-ball pressure, energy, and enthusiasm. The Celtics forced 14 second-half turnovers, and those two were on the frontlines.

Pritchard, who has only been pushed into action because Malcolm Brogdon remains sidelined with hamstring tightness, continues to show that he belongs in the regular rotation even when this team is at full strength. He had 10 points, 4 rebounds, and 2 steals in just 14 minutes, and with the Celtics teetering at the end of the third quarter he had an essential stretch in which he drilled a 30-foot 3-pointer and came up with a steal before coasting in for a layup at the buzzer. That helped slice what once was a 90-75 deficit to a considerably more manageable 96-89.

White had 16 points, 5 assists, and 4 of his team’s 15 steals. The Celtics outscored the Thunder by 21 points during White’s 33 minutes, 23 seconds on the floor, and it felt like it.

“We were on the bench there and we all kind of looked at each other like, ‘We’ve got to change the energy of the game,’ ” White said. “That’s what our job is as a bench unit, and I think we did a good job of going in there and kind of turning the game.”

Added Mazzulla: “I think it goes back to focusing on our depth. We have the humility to understand we can play in a different way. When someone doesn’t have it, the next guy’s got to be ready to bring it. I thought that’s what we did.”

The game’s end, meanwhile, belonged to Smart. Saddled with foul trouble for parts of the night, he checked back in with 8:03 left and finished the Thunder off by making all four of his shots and tallying 10 points, 3 rebounds, and 4 assists. He took just two 3-pointers in the game and said that in the second half he received a tip from veteran forward Blake Griffin, who pointed out that the Thunder weren’t paying much attention to him when he pushed into the paint.

“I just stayed aggressive and realized that I had the advantage,” Smart said. “Jayson and Jaylen had it going, but we all know all eyes are going to be on them every night. So in times like this, the floor opened up for me and I just have to make the right read, and tonight it was for me to score the ball.”

With the Celtics clinging to a 113-112 lead, Smart drilled a jumper from the left corner with 3:04 left. After Lu Dort tied the score with a three-point play, Tatum had the ball knocked away and it ended up in the hands of Smart, who hit a deep 3-pointer.

Smart hits a three pointer over Oklahoma City's Luguentz Dort to put Boston ahead, 118-115, late in the game.Jim Davis/Globe Staff

Shai Gilgeous-Alexander, who erupted for a game-high 37 points, pulled the Thunder back within 121-118 before Smart whirled through the lane and converted a tough layup that stretched the lead to five with 37.8 seconds left.

“I think it was just good for us to face some adversity and figure it out,” Tatum said. “Everybody contributed.”