BOSTON -- The Boston Celtics played terribly for a stretch in the second half. It didn't matter because they made everything look easy the rest of the time.
"We played 14, 16 minutes of bad basketball," Boston coach Brad Stevens said. "You go through so many of these situations in the year. I was happy with how we responded."
Trailing 70-49 midway through the third quarter, Philadelphia took advantage of Boston's ice-cold shooting and rallied to make it 83-80 on Hollis Thompson's 3-pointer with 7 1/2 minutes to play.
But the Celtics took charge with an 8-0 run -- the final points coming on Sullinger's three-point play with 5 1/2 minutes left.
Sullinger could even smile when he was asked why Boston blew the big lead.
"You see how many leads we've blown early in the season. We're kind of used to it," he said. "We know how to respond and we responded well."
Sullinger was back in the starting lineup after being yanked the previous two home games for arriving late to the arena for pregame activities.
Luc Mbah a Moute led the 76ers with 18 points, while Thompson and Robert Covington had 16 apiece. It was Philadelphia's eighth straight road loss.
Boston has won all three meetings with the 76ers this season by double digits.
With the Sixers missing Michael Carter-Williams, their top player and only true point guard, due to a right toe injury, Boston jumped out to a 26-point lead midway through the second quarter before Philadelphia used a big third period to close the gap to six.
"We just tried to remember who we were even though we didn't have any point guards," Philadelphia coach Brett Brown said. "We had no idea what we were doing in the first period. We started so poorly that it spun off in a number of areas."
Boston scored the initial nine points of the game -- with Bradley getting the first seven -- and opened a double-digit lead just 6 1/2 minutes in.
The Celtics shot 57.9 percent in the first quarter and led 29-15. They started the second by scoring 16 of the first 20 points, opening a 45-19 edge on Jae Crowder's layup.
At times, Boston was practically toying with the 76ers, passing the ball around the perimeter a couple of times before taking uncontested jumpers or scoring on easy drives to the basket.
"We fought all the way back," said 76ers rookie guard Tim Frazier, who signed a 10-day contract on Wednesday. "We battled. We wanted the win."
Boston shot 54.8 percent (23 of 42) and led 60-42 at halftime. The 76ers were also outrebounded 26-16.
The Celtics pushed it to 70-49 before Philadelphia closed the third quarter with a 20-5 run, slicing the deficit to single digits for the first time since the opening minutes. Boston led 75-69 after three.
76ers: Brown said Carter-Williams will be a game-time decision Saturday against Charlotte. "We will err on the side of being smart and conservative with him," Brown said. "I would be surprised if we play him tomorrow." Without Carter-Williams, the 76ers didn't have a true point guard available. "It's the reality of our team, getting ready for All-Star break and having the flexibility with potential trades before the trade deadline, and it's resulted in this point guard drought at the moment," Brown said.
Celtics: G Evan Turner visited some of his former teammates in the 76ers' locker room about 90 minutes before the opening tip.
Miss Massachusetts, Lauren Kuhn, stopped singing the national anthem twice. When she paused the second time, the crowd jumped in and sang with her, guiding her to the finish. "I love these fans," Crowder said. "They helped her out."
Frazier, signed from the NBA Development League, had 11 assists in 34 1/2 minutes. He was undrafted. "Didn't (feel real) until I got on the court," he said.
76ers: Host Charlotte on Saturday.
Celtics: At Milwaukee on Saturday.
Jim Boylen picked to coach USA Basketball in World Cup qualifiers
Jim Boylen, who most recently coached the Chicago Bulls from 2018-20, will coach Team USA next month in the first window of qualifying for the 2023 Basketball World Cup.
NBA's 75 greatest players of all time: The complete list so far
The first 50 players on the league's list of the NBA's 75 greatest have been unveiled.
Doc Rivers calls Ben Simmons drama 'no fun'
76ers coach Doc Rivers expresses his feelings about the situation with Ben Simmons.