KISSIMMEE, Fla. – The Boston Celtics have a lot of praise for Al Horford.

That’s not surprising, considering he was one of their team leaders the previous three seasons. They know firsthand how much of an impact the post player can have in big games. And they have paid attention to his role since he was inserted back into the 76ers’ starting lineup after Ben Simmons’ knee injury on Aug. 5.

Now the Celtics must find a way to limit the man they’re fond of in an opening-round playoff series inside the NBA bubble at Walt Disney World. Game 1 of the best-of-seven series starts at 6:30 p.m. Monday.

“Al knows how to play,” Celtics coach Brad Stevens said. “He’s an excellent player on both ends. He understands what they are trying to accomplish as a team.”

Horford helped lead Boston to consecutive Eastern Conference finals appearances in 2017 and 2018. The 34-year-old also garnered his fifth All-Star selection as a Celtic two seasons ago. One can argue that he kept them together in the postseason.

“Watching Al for the last couple of years was great,” Semi Ojeleye said. “Playing against him is going to be good as well. We have to be ready. "

Horford is at his best while quarterbacking from the post. He has also found his groove playing alongside Embiid of late.

The belief was that Embiid and Horford couldn’t coexist. However, the problem came about when Embiid, Horford, and Simmons were on the floor at the same time. One can argue the spacing was bad because Simmons was hesitant to shoot from the perimeter. So opponents packed the paint.

The spacing wasn’t a problem in Horford’s first game back in the starting lineup on Aug. 7. With Simmons out, he and Embiid played well together in a 108-101 victory over the Orlando Magic. Embiid finished with 23 points and 13 rebounds, while Horford had 21 points and nine rebounds.

The duo also played well together against the Detroit Pistons on March 11 in the Sixers’ final game before the NBA shutdown. Embiid had a team-high 30 points to go with a game-high 14 rebounds after missing the previous five games with a left-shoulder sprain. Horford had 20 points, 10 rebounds, 6 assists, and 2 blocks. That marked the eighth and final game that Simmons missed with a pinched nerve in his lower back.

“We know he’s a high-caliber player who can hurt you in the post or from the outside,” Ojeleye said of Horford. “So we have to prepare for him especially. He’s a big part of their team, so we have to know and be aware that he’s going to be involved in a lot of what they’re doing.”

Horford averaged 14.0 points, 6.3 rebounds, and 4.3 assists in his three games against the Celtics this season. The Sixers have won three of the teams’ four regular-season meetings.

The Celtics head into the playoffs with a 48-24 record. The Sixers took a 42-30 mark into their seeding-games finale Friday against the Houston Rockets at The Arena.