PHILADELPHIA — After Saturday’s Game 3 overtime win over the 76ers, Brad Stevens spoke not just of Al Horford’s brilliant play — seven points, two rebounds, a steal and a block in OT — but even more of his calming effect.

Horford is the Celtics’ breakwater as the playoff seas rise and whitecaps appear atop the waves. Stevens said he stills the coaches as well as his teammates. Some front office people, too.

Assistant general manager Mike Zarren is a bit skittish by nature.

“I wouldn’t say skittish,” Zarren said after yesterday’s practice at Temple University. “Skittish implies fear. I don’t have fear. Let’s just say I’m jumpy.”

Which is why he appreciates Horford.

“You come into the locker room after the game and everyone’s going nuts, and Al just stands there and nods and smiles and gives you five,” Zarren said. “He’s just solid all the time, and that’s hard to find. He’s never too high, never low. He’s just a stabilizing force for this whole team.”

The task for the Celtics heading into this evening’s Game 4 is avoid getting lost in the clouds. They possess a 3-0 lead, and while Sixers coach — and Portland, Maine, native — Brett Brown may preach the tale of the 2004 Red Sox against the Yankees in the ALCS, no NBA team has ever come back from such a deficit to win a series.

Horford would rather the Celts not give anything away just because they can. They have four putts to win the series, and while that is certainly an enviable position, this Eastern Conference semifinal isn’t over until the golf ball sits in the bottom of the cup.

So sayeth Oracle Al.

“You just break it down,” Horford told the Herald yesterday. “The first message was have a good practice, and we did that. We just have to come out with that same focus (tonight), and we have to be better executing on offense. If we do that, I think we have a good chance.

“I think the way we look at it is that we just try to focus on this game itself. You know, we can’t get caught up in where we are in the series right now. I think we need to go out there and just play and not think about that. If we play the right way, we’ll put ourselves in a good position.

“We’re coming off an emotional game, so I was encouraged seeing our guys so locked in for practice.”

Horford, too. After the team workout, he went through a shooting drill and spent another five minutes warming down. People noticed. People always notice.

“He steps in and says things sometimes,” said rookie Semi Ojeleye. “But it’s not just what he says. I think one of his biggest effects is that we just get to watch him. With someone like Al, you just see how he goes about his business. It’s a great example for everyone.”

Experience has been a hot topic in this series, and Horford’s supply is illuminated in comparison to his young mates and opponents. This is his 11th year in the league and 10th in the playoffs. Meanwhile, Jayson Tatum is averaging 24.3 points against the 76ers, and he was a teenager until March.

“It helps, but honestly I just think that if we’re all locked in and we know what we need to do, our guys have shown that we can overcome some of those experience things,” said Horford. “For us, we just have to get good shots and do things the right way. I think that’s where our experience can become an issue for us. We can get a little trigger-happy and take bad shots. But I think that, as far as defensively and the things we can control, I think the experience thing is overrated.”

Then again, Philly’s Ben Simmons and Joel Embiid have gotten flustered at times, committing turnovers and forcing shots to help the Celtics get to 3-0. And Brown has pointed out on more than a few occasions that these are events his young stars must endure.

“In that sense, yes,” said Horford. “Playing in a lot of big games and understanding what it takes to win, it definitely helps.”

But Experienced Al believes he was ready from the jump.

“You know, I was very lucky in college to play in meaningful games, in Final Fours and things like that. And going into my first playoffs, I was ve-ry confident,” said the Florida product, drawing out the ‘very.’ “I was very relaxed. Even thought it was a different experience and environment, I felt what I’d been through in college helped me.”

But all this talk of wisdom and the like has become a euphemism for, you know, old. People are making the 31-year-old Horford out to be Methuselah.

“Right?” he said with a laugh. “I mean, I understand I’m not 20, but I’m not 40, either. But I think people look at me like I’m 40. But it’s fine.”

So are the Celts — with Horford’s influence. Even the “jumpy” one?

“No,” Zarren said with a laugh. “I’m still really excited. It takes more than that.”