BOSTON -- Any discussion about the Boston Celtics over this holiday weekend was centered around the team meeting that took place after Friday's dismal showing at home against the Milwaukee Bucks.

There was plenty more talk about it after the Celtics came out and blew the doors off the Charlotte Hornets Sunday night, winning 119-103 here at TD Garden in a game that wasn't nearly that close. But what had a far bigger impact on the Celtics than a team meeting -- both Sunday night and moving forward -- was the return of Al Horford after a seven-game absence with a knee injury.

"You take a lot of comfort in having him out on the floor," Celtics coach Brad Stevens said. "There's no question about that."

It was fitting that Horford made his return amid the hubbub about meetings, and alongside another starter, Marcus Morris, who also sat out the prior two games with a knee issue. There isn't a more understated star in the league -- both in his play on the court and his conduct off of it -- and thus flying under the radar suits him just fine.

His impact on the Celtics, though, can't be overstated.

Al Horford returned with a minutes restriction Sunday against the Charlotte Hornets. Bob DeChiara/USA TODAY

Horford has always been a player, going back to his first days in the league with the Atlanta Hawks more than a decade ago, who has filled in whatever gaps his team has needed him to. That's no different in Boston, where Horford provides the Celtics with both elite passing and spacing at the center spot offensively -- not to mention marshaling a defense that once again ranks among the NBA's best.

His presence was a big part of why the Celtics beat the Bucks here in Boston on Nov. 1 -- and it was no coincidence things were much different without him spacing the floor and contorting Milwaukee's defense Friday night. Ditto Boston's mastery over the Philadelphia 76ers the past two years -- and why his return, coming on the eve of Boston's rematch with Philadelphia in a Christmas Day showdown, couldn't have come at a better time as far as the Celtics are concerned.

"It's tough when there are so many guys in and out of the lineup and so many things [changing]," Horford said. "It puts a lot of pressure on some of our guys, so it's just good we're getting healthy. Marcus Morris being back, that's huge for us, me being back obviously. [Aron] Baynes is out now but at least we are getting healthy again, so that is all going to help our offense, and help our team."

There have been plenty of things contributing to Boston's wild swings back and forth throughout this season thus far. Arguably the biggest, though, has been Horford's play. When he plays well -- as he did in Boston's run to the brink of the NBA Finals last season without Kyrie Irving and Gordon Hayward -- the Celtics are a far different team. This season, though, he has looked hampered by his balky knee, which Boston labeled as patellofemoral pain syndrome during his recent seven-game hiatus.

Between Philadelphia's Joel Embiid, Milwaukee's Brook Lopez, Toronto's Serge Ibaka and Jonas Valanciunas, and Indiana's Myles Turner and Domantas Sabonis, each of the other contenders in the East has weapons at the pivot that Boston will need Horford to square off against -- and, often, get the better of -- if the Celtics want to be the team they were expected to be before this season began.

To that end, perhaps the single most important thing to come out of Sunday's game wasn't the win to snap a three-game losing skid, or even Horford playing well -- he put up 10 points while making all four shots he took to go with six rebounds and five assists in 19 minutes -- but that he emerged from the game with his knee still feeling good.

"It was very helpful having that time off," he said. "I'm just happy that I was able to go out there and play with a lot of energy. It's just good to be back. Sitting on the sidelines is tough, not being able to be on the court helping the guys.

"I'm just happy to be back playing."

On to something... Al Horford's return means the Celtics are back to using a starting lineup of Kyrie Irving, Marcus Smart, Jayson Tatum, Marcus Morris and Horford. Boston is undefeated this season with that lineup, while the Celtics were only 7-6 with the opening night lineup of Irving, Jaylen Brown, Tatum, Gordon Hayward and Horford. Celtics lineups Smart/Morris Brown/Hayward W-L starters 4-0 7-6 Minutes 93 139 Off. Eff. 123.1 91.2 Def. Eff. 104.1 94.7 Net Rating 19.0 -3.5 >> Both lineups include Kyrie Irving, Jayson Tatum, Al Horford

The Celtics are just as happy to have their security blanket at center back, too. And, with the next several games featuring matchups with the Sixers (Embiid), Houston Rockets (Clint Capela), Memphis Grizzlies (Marc Gasol), San Antonio Spurs (LaMarcus Aldridge), Minnesota Timberwolves (Karl-Anthony Towns) and Dallas Mavericks (DeAndre Jordan), Horford will have plenty of work to do, too.

No matchup will garner more scrutiny than Tuesday's holiday matchup with Embiid, though. After the Celtics, who beat Philadelphia in five games in the Eastern Conference semifinals last season, beat the Sixers again on opening night, Embiid declared that Boston can't be a rival -- because Philadelphia can't beat the Celtics.

"This is not a rivalry," Embiid said. "I don't know our record against them, but it's pretty bad.

"They always kick our ass."

Horford has been no small part of that success. He averaged 16.3 points, 7.0 rebounds and 4.5 assists while shooting 49 percent from the field and 41 percent from 3 against Philadelphia in four regular-season games, and then shot over 56 percent against the Sixers in Boston's five-game series victory.

Embiid, meanwhile, averaged 23 points in that series, but needed 21 shots per game to do so -- which is exactly what he did in Philadelphia's season-opening loss here between the two teams.

"It's great," Horford said of going up against Embiid. "I have a lot of respect for Joel. I've always been a big fan of his game, and just how he is. He's a guy that you want to see play, and I feel like you want him around you, right?

"It's one of those games we are lucky to be one of the few teams playing on Christmas Day, and it is nationally televised. It's one of those fun games, and we're here at home, so it's good for us."

What's better for the Celtics is that they'll have Horford on the court for it. Whether Boston can keep things that way moving forward will have a far greater impact on this team, and its season, than any discussion ever could.