PHILADELPHIA -- In the first two meetings between the Boston Celtics and Philadelphia 76ers this season, the Sixers bludgeoned the Celtics into submission.

Those games, though, featured superstar center Joel Embiid, one of the league's biggest and heaviest objects. Boston had been helpless to stop him. But Embiid wasn't on the court Thursday night. Instead, he was on his way to New York, where he'll have surgery on his dislocated left ring finger Friday.

So, with Embiid out of the lineup, things would go differently for the Celtics ... right?

Not exactly.

"I think the big picture [difference] is just matchups-wise with the guys that they have, and the size and scoring ability that we have," Sixers forward Tobias Harris said.

After the Sixers came away with a 109-98 victory over the Celtics, one thing is clear: Whether Embiid is healthy or not, the Celtics have a Sixers problem.

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The reverse was true the past few seasons, but now the player who caused Philadelphia so many of those problems -- Al Horford -- is wearing a Sixers uniform.

It has been an awkward season for Horford in Philadelphia. He and Embiid have struggled to coexist on the court. He has looked uncomfortable shifting away from the things that made him one of the NBA's most versatile big men and a player the Sixers were intent on adding this offseason.

But with Embiid sidelined, Horford was back to playing center full time. He put up precisely the kind of game that he had so many times the past three years for Boston, finishing with 17 points on 7-for-11 shooting to go with 8 rebounds, 6 assists, 1 steal and 2 blocks. The 76ers outscored the Celtics by 19 points in Horford's 32 minutes on the floor.

"Coming here, I expected to play the 4, but I know one of my strengths as a player is to play inside, play outside, play the 4, play the 5, guard different positions on the court, and I was expecting that," Horford said. "I knew wherever I'm needed, that is one of the strengths that I bring, to be able to do different things."

Horford repeatedly outmuscled former understudy Daniel Theis inside, grabbing five offensive rebounds. His passing helped unlock a Philadelphia offense that went 11-for-27 (40.7%) from 3-point range. By shifting around the defensive coverages to accentuate Horford's strengths, as opposed to Embiid's, the Sixers forced the Celtics into 50 misses on 88 shots, erasing an early 15-point deficit.

"I thought they just physically wore on us," Celtics coach Brad Stevens said.

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That was especially true of Ben Simmons, who got whatever he wanted. It was a far cry from the playoff series two years ago in which the Celtics exposed Simmons' lack of a jump shot. He didn't need one Thursday night, repeatedly bullying the Celtics in the paint. He was able to get a baby hook shot whenever he wanted, and he said afterward that he "definitely" sought to post up more with Embiid out of the game.

Anyone watching the game couldn't help but notice Simmons was able to do what he wanted physically no matter who was guarding him.

"I mean, he does that all the time," Harris said with a smile.

He isn't wrong. But sometimes, with all of the noise that surrounds Simmons -- and particularly that lack of a jump shot -- it is easy to forget everything that he does do. And, in this game, he showcased almost all of it, including playing a few minutes at center when Horford was off the floor. That's the advantage Philadelphia has with a 6-foot-10 point guard; even without Embiid, the Sixers still are bigger than the Celtics at just about every position.

Simmons smothered the Celtics defensively, including poking the ball away from Kemba Walker for a steal at a key moment midway through the fourth quarter. And Sixers coach Brett Brown allowed Simmons to push the pace in a way Philadelphia simply can't when Embiid is around, to the benefit of all involved.

"Just imposing his will," Horford said of Simmons. "He's very gifted physically and made some good moves in the post, pushing the pace.

"It's tough to guard him in the open floor. I think his energy, with that, it's contagious, and it gets us all going. And, obviously, that was the difference."

Thursday also served as a reminder of how quickly things can change in the NBA. A week ago, the Celtics were riding high, winning eight out of nine games and looking as if they might settle into the second seed in the East. The Sixers, meanwhile, lost in Houston last Friday to drop their fourth straight game. After that loss, Embiid said all of the losing was taking a toll on him.

Now the Sixers have won two games in a row against playoff-bound opponents -- the Thunder on Monday and the Celtics on Thursday -- and Boston is in the midst of its first three-game losing streak of the season. The Celtics also have officially lost the season series to the Sixers thanks to Thursday's loss, something that could come into play as a tiebreaker in April.

"Nobody wants to lose," said Celtics guard Marcus Smart, who scored 24 points off the bench. "And everybody is trying to figure it out. ... It happens. We've just got to be ready to turn it around and keep playing. That's the only way."

The Sixers are still trying to figure things out too. While some pieces might fit better without Embiid on the court, that doesn't mean Philadelphia is better off without its best player.

"The few of us knew that since he wasn't playing, we were going to have to be more aggressive because he is quite possibly the best center in the game and he's a huge piece of our offense," said Josh Richardson, who scored 14 of his game-high 29 points in the fourth quarter to help close out the Celtics. "We knew that it's kind of a mental note that you have to take going into it. I knew early on that I was going to have to be aggressive to give our offense a good shot."

With Embiid out for a while -- the team said Thursday that he will be reevaluated in one to two weeks -- the Sixers will have to continue to create positive trends during his absence. One of them should be the improved play from Horford. Another is further developing an identity in the minutes when Embiid is off the court, and when Simmons is out there with Horford.

Whether that happens or not, the Sixers can feel good about how they match up with the Celtics. If there was any doubt about that before Thursday night, it's gone now.