The underdog Magic made the Celtics sweat Sunday in Game 1 of their first-round playoff series. They even held a halftime lead at TD Garden.

But Orlando lost steam in the second half, and Boston surged ahead, turning a competitive game into a 103-86 romp.

Derrick White delivered one of the best postseason performances of his career for the defending champs, leading the No. 2 seed Celtics with 30 points on 10-of-18 shooting and going 7-of-12 from 3-point range. Payton Pritchard was a difference-maker off the bench with 19 points in 25 minutes, and Jrue Holiday spearheaded a dominant third quarter that permanently shifted momentum toward Boston.

Jayson Tatum turned in a 17-point, 14-rebound double-double despite shooting the ball poorly (8-for-22, 1-for-8 from three, 0-for-4 from the foul line). Jaylen Brown tallied 16 points (6-for-14), five rebounds, two assists and two steals in 31 minutes in his return from a lingering knee injury. Kristaps Porzingis finished with five bounds on 1-of-8 shooting in a quiet outing from Boston’s starting center.

The seventh-seeded Magic got strong outings from stars Paolo Banchero (36 points, 11 rebounds) and Franz Wagner (23 points, five assists, two blocks) but little from their supporting cast. The rest of their roster combined for just 27 points, continuing a season-long trend for one of the NBA’s least efficient offenses.

Game 2 is Wednesday night on Causeway Street.

“That’s the great thing about playoffs,” said White, who entered Sunday with just two career 30-point games in the postseason. “It doesn’t matter what you do in Game 1; you’ve got to be even better next game. So we’ve got to get ready for that challenge.”

Brown, playing in his first game in 12 days, looked spry early for Boston. In the opening six minutes, he shot past Magic center Wendell Carter Jr. for a layup, dished a drive-and-kick assist to White for a corner three and drove through contact to finish at the rim against Kentavious Caldwell-Pope and Anthony Black.

After Wagner responded to Brown’s second layup with a 3-pointer, Brown intercepted a cross-court Wagner pass, fed the ball between his legs to a trailing Holiday and corralled an offensive rebound after Holiday couldn’t convert, leading to another White three. Seconds later, Brown stepped in front of Carter and drew an offensive foul.

“I trust Jaylen,” Celtics head coach Joe Mazzulla said. “… He knows how to take care of himself. He knows how to get to the spots that he needs to get to. To me, it’s more he’s getting better and better, even defensively from the physicality standpoint. He had some great possessions being careful there in the first half. He’s right where he wants to be. He’s right where we need him to be, and we’re going to continue to rely on him.”

Pritchard checked in with 1:50 remaining in the first quarter and made an immediate impact. In his first three minutes of floor time, he scored nine points, hitting a pair of 3-pointers and making all three free throws after being fouled on another. Pritchard’s second triple followed a seismic block by Porzingis, who sparked a fast break by emphatically rejecting a Cole Anthony jumper.

Less than two minutes later, Pritchard cooked Anthony on a drive to the rim, using a nifty hesitation move to zip past the Magic guard. On his next drive, Pritchard drew three Orlando defenders before kicking out to White for an open three.

That shot put Boston ahead 39-28 with 7:31 to play in the first half. That’s when the Magic’s much-maligned offense got hot. Orlando, which made an NBA-low 11.1 3-pointers per game during the regular season, hit five during one six-minute stretch, including two by the typically erratic Banchero, who led all first-half scorers with 19 points. The Celtics, meanwhile, made just one field goal in the final 4:30 of the second quarter. The Magic closed the half with a 21-9 run and led 49-48 at the break.

Boston shot a solid 43.8% from deep in the first half but did so on just 15 3-point attempts, tied for its fewest in any first half this season. Chasing shooters off the 3-point lane is a defensive priority for the Magic, who also allowed the fewest made threes per game this season. It was an unbalanced shooting performance, as well, with White, Pritchard and Al Horford accounting for all seven of the Celtics’ first-half made threes. The rest of their roster was a combined 0-for-6.

That changed early in the third quarter when Holiday drilled a pair of threes, both in transition, to help Boston rebuild a double-digit lead. The veteran guard, whose clutch plays at both ends were pivotal during the Celtics’ 2024 championship run, played the entire quarter and was excellent throughout, scoring or assisting on seven of the Celtics’ 10 made baskets.

Holiday had nine points, two steals and four assists in the third, including one on White’s fifth 3-pointer of the game and another on a soaring lob dunk by Brown. Brown and Tatum asserted themselves late in the quarter, scoring Boston’s final 12 points, all on shots at the rim or free throws.

“He’s an innate competitor, and sometimes he takes a back seat because of the type of guys that we have,” Mazzulla said of Holiday. “I thought tonight, he put the team on his back from that passion and emotion standpoint, and that’s why Jrue Holiday is Jrue Holiday. So we’re lucky to have him. We’re going to need that every single night. But we do feed off his physicality and his presence.”

The Celtics appeared to take a 78-65 lead into the fourth quarter. But after a media timeout, officials called for the final 0.5 seconds of the third to be replayed, ruling after a video review that Brown fouled Wagner just before the buzzer. Wagner made both of his free throws to trim two points off Boston’s cushion.

White and Prichard quickly restored and then expanded that lead, however, by erupting for 11 points over the first five Celtics possessions of the final quarter. The second of back-to-back threes by Pritchard put Boston ahead 89-71, and the Celtics held a comfortable edge the rest of the way.

Boston outscored Orlando 26-4 in transition and 24-8 off turnovers, upping its pace and physicality to overcome its halftime deficit.

“I think that in the first half, they kind of controlled the intensity level of the game,” Brown said. “They were more physical than us. And in the second half, we kind of shifted that. We’ve got to have that mentality all series long. We gotta have the 100 mentality, be more physical, set the tone, set the intensity of the game. I think Orlando did a great job of that in the first half, so, it’s going to be a lot of that this series. (We) can’t expect nothing less. It’s going to be more of a fight than it is skill. Our guys gotta be ready to fight.”

Tatum experienced an injury scare during the fourth quarter when Caldwell-Pope dropped him with a flagrant foul under the basket. The Celtics star landed on his wrist and stayed down for an extended period, but he remained in the game, only exiting when Mazzulla emptied his bench with 1:14 remaining. A postgame X-ray came back “clean,” said Tatum, who was a game-best plus-23 in the win.