ORLANDO — A sluggish start and sloppy finish doomed the Celtics on Friday night in a 123-110 loss to the Magic.

Jaylen Brown scored a game-high 32 points to lead Boston, but nearly all of those came in the first three quarters. Payton Pritchard added 27 points on 8-of-16 shooting, Derrick White tallied 16 points and 10 assists, and Anfernee Simons bounced back from an ugly first quarter to score 11 points in the fourth, including a go-ahead 3-pointer with 7:23 remaining.

The Magic, bested by Boston in a five-game opening-round playoff series last spring, controlled play from that point forward, rebuilding a double-digit lead with just under two minutes to play. And because this was an NBA Cup game, with a potential point-differential tiebreaker looming at the end of group play, Orlando continued to attack until the final buzzer, scoring an extra eight points in the last 67 seconds.

The loss dropped the Celtics to 4-6 on the season and 1-1 in NBA Cup group play. They’ll face the Magic again in a non-Cup game Sunday at the Kia Center.

”It was a good game, and the effort and physicality was there,” Celtics head coach Joe Mazzulla said. “We just have to be able to execute on both ends of the floor throughout a close game.”

The Celtics’ starting five, intact for the seventh consecutive game, came in with a sterling 98.4 defensive rating, the second-best of any NBA grouping that had logged at least 50 minutes together. But that group struggled to contain the Magic in the early going.

After 3-pointers by Josh Minott and Pritchard gave Boston a quick 10-5 lead, Orlando proceeded to score on seven straight possessions against the Celtics’ starters. Then, after a Mazzulla timeout and a round of C’s substitutions, the Magic got back-to-back buckets off offensive rebounds, then two makes off steals by Desmond Bane (27 points) and Paolo Banchero (15 points).

Simons was the offending party on Bane’s swipe, and he was beaten for an and-one dunk in transition shortly thereafter. Those miscues got Boston’s sixth man pulled from the floor after two minutes, during which the Celtics were outscored by 11 points. He sat out the rest of the first half.

Orlando also hit five of its first six 3-pointers to power a 24-4 first-quarter run. The Magic made 17 threes in the game — well above their season average of 10.4 — at a 47.4% clip. The Celtics, well aware of Orlando’s identity as a hyper-physical team that annually ranks near the bottom of the NBA in 3-point volume, weren’t prepared for that onslaught.

“They were just hitting threes,” Pritchard said. “They’re not known for that. So we were in the paint, and for the most part, we were living with those guys shooting. They hit some with contest, and they were just hitting some of those tonight.”

A new-look Celtics lineup featuring Pritchard, Hugo Gonzalez, Jordan Walsh, Sam Hauser and Luka Garza — five players who did not play a minute together in Boston’s first nine games — stopped the bleeding late in the first. Walsh, coming off by far his best outing of the season in Wednesday’s win over Washington, then remained in the game with starters White, Brown, Minott and Neemias Queta as Boston opened the second quarter with a 14-5 run that cut Orlando’s double-digit lead to four.

After rarely playing outside of garbage time before this week, Walsh has made an impact with his defensive pressure in back-to-back games. In this one, he tallied five rebounds, two offensive boards, one steal and one block before halftime.

Brown, Pritchard and White combined to score 22 of the Celtics’ 26 second-quarter points. The Magic maintained a 59-51 lead at half, but Boston pulled even early in the third after Minott drew a foul on an aggressive crash, and Pritchard picked Bane’s pocket and canned a three.

Then, Brown took over. Midrange jumper. Midrange jumper. Drive. Drive again. Back to the midrange. He made seven consecutive field goals to score 14 straight Celtics points, reaching the 30-point mark before the end of the third quarter.

Brown became just the fourth player in Celtics history to score 30-plus points in six of the first 10 games of a season, joining Sam Jones, John Havlicek and Jayson Tatum in that exclusive club.

After Brown’s scoring binge kept the Celtics competitive, a redemptive effort from Simons gave them their first lead since the opening minutes. He hit three straight shots, including a pair of 3-pointers, to put Boston up 94-93. Active rebounding by Walsh and Gonzalez set up Simons for his go-ahead triple.

“I think J-Walsh and Hugo came in and changed the game for us, got us back into the game,” Simons said when asked about his quick first-half hook. “I think it was pretty much that simple. All you could do is control what you control, and when you get out there, do your best to impact the game. And I think J-Walsh and Hugo were doing the best at that. They got us back in that game with all the energy plays and stuff like that, so it’s really that simple to me.”

Orlando dominated the home stretch, however, by capitalizing on a string of Celtics errors. Chief among them: two Minott giveaways; an open layup that Queta couldn’t convert, followed by a transition take foul in the backcourt; and a Pritchard turnover that led to a fast-break and-one finish by Carter. The latter put the Magic ahead 112-100 with 1:23 to play.

The Celtics committed 11 fourth-quarter fouls, including one drawn charge attempt by White that was overturned after a successful Orlando challenge. The Magic shot 31 free throws in the game to Boston’s 16, with Brown — highly effective at drawing contact on drives and pull-ups this season — getting to the line just twice.

Brown also managed just two points in the fourth quarter, which he seemed to view as punishment from the officiating crew for his harsh criticism of a blown late-game call in Monday’s loss to Utah.

“In the fourth quarter, I think the officials made their point,” said Brown, who finished as a game-worst minus-21 in 36 minutes. “So I get it. I’ll keep my mouth closed.”

Other observations:

— Despite their late lapses, the Celtics were encouraged by how they matched the Magic’s physicality. The teams finished dead even in rebounds (44-44) and points in the paint (44-44), and Boston grabbed one more offensive rebound (12-11).

“I’m proud of how we fought back, stayed in it, because it’s a team that kind of punks us on the boards, is way more physical,” Pritchard said. “I didn’t feel like we got out-physicaled. I felt like, you know, they hit threes. They weren’t a team that was supposed to be a high-shooting 3-point team, and we kind of were living with that. Tip the cap, they made threes tonight.”

— The only Celtics players to finish with positive plus/minuses: Walsh, Gonzalez and Queta.

Queta (plus-7 in 30 minutes) leads all Boston players in that metric this season and also entered Friday with the NBA’s second-best net rating. The center went 2-for-8 in the loss but had eight rebounds, two blocks, one assist and one steal.

“He’s gotten better, not only from the time that he’s been here in his career, but also he’s gotten better from training camp to preseason to where we’re at right now,” Mazzulla said pregame. “We are a better team when he’s on the floor. He understands that responsibility and also the execution of that. He’s a guy that just keeps getting better and better.”

— Magic head coach Jamahl Mosley said pregame that there was still “a little bit of tension” between the teams after their brawl of a first-round playoff series last spring, but this rematch was light on extracurriculars. There were no flagrant or technical fouls on either side, though Gonzalez did catch Franz Wagner (22 points) in the face on one rebound attempt.

— The Celtics will play their final two NBA Cup group play games later this month at TD Garden. The Brooklyn Nets will visit on Friday, Nov. 21, followed by the Detroit Pistons on Wednesday, Nov. 26.