Al Horford fitting in quite nicely

Al Horford has had an immediate and profound effect on the Celtics lineup.JESSICA HILL/ASSOCIATED PRESS

So far, the acclimation of Al Horford to the Celtics’ team concept has been a resounding success.

Not that there was much concern about whether the selfless Horford, who has been a model professional throughout his career, would fit in. But the Horford effect has been immediate and profound, giving the organization confidence as it approaches a critical season.

The Horford signing was supposed to bring stability to the Celtics’ frontcourt, the addition of a defensive stalwart with a high basketball IQ and the ability to protect the rim and stretch the floor with good perimeter shooting. The Celtics haven’t had a player this intelligent since Kevin Garnett, and Horford’s presence has had an immediate impact.

In his two preseason appearances, Horford is a plus-42, as the Celtics starters dominated in their stretches against the 76ers and Hornets. The fact that the starters — Isaiah Thomas, Avery Bradley, Jae Crowder, Amir Johnson, and Horford — have blended well together is not a surprise. It’s how quickly they’ve done it that is the stunner.

“That’s encouraging,” Horford said. “We still have some work to do, but I just feel like these guys here have made it easy for me. I’m just kind of playing my game. Isaiah has given me the ball at the right times. So has Avery. They’re finding me in different ways, so for me it’s just getting used to playing the style that we’re trying to play. It’s only two games, but it looks good.”

It’s important for the Celtics to get off to a fast start this season. Besides Horford and Gerald Green, the majority of the roster returns. They are all familiar with one another. They have developed a bond, and if the preseason is any indication, it appears Terry Rozier, James Young, and Marcus Smart have improved their games and are prepared for bigger roles.

That development is what president of basketball operations Danny Ainge envisioned when he utilized all of those draft picks gained from the Brooklyn Nets and through the 2013-14 rebuilding season. The addition of Horford and Green, along with the ascension of the younger core, makes the Celtics a legitimate contender in the Eastern Conference.

There was a great deal of concern about who would fill the Evan Turner role on offense. Turner, who signed a four-year, $70 million contract with the Portland Trail Blazers, was the team’s most versatile player and point forward. The Celtics have sought this preseason to find his replacement by committee.

Smart, entering his third NBA season, is the most likely candidate. Coach Brad Stevens allowed him to start at point guard in Saturday’s win, giving him an opportunity to display his ability to distribute the ball and run the team. Smart finished the game with 9 points, 5 assists, and 5 rebounds in 25 minutes.

“Every day in the preseason is a practice,” Stevens said. “It’s a great chance for the young players to get a chance to play more. And it’s a great chance for our older guys to impact the game vocally. It’s a positive for everybody if you play the right way.”

Thomas said he has noticed the immediate chemistry, especially from the starting lineup. In both appearances, the starting five has dominated, especially with ball movement and spacing.

“Our pace and just our unselfishness,” Thomas said of the improvement. “We’re looking to get not just a good shot but a great shot. The ball is just going from side to side. It’s not holding and staying in one place. And it’s being effective. We’ve got guys out there that are in the right spots and more comfortable in their role.

“And I keep saying it, but Al makes it that much easier because he knows how to play.”

Horford has repeatedly said that his new environment has been welcoming. The Celtics haven’t asked him to be anything more than what he is, and that has made the landing even softer.

“A lot of times you catch yourself thinking out there, but Isaiah is doing a good job of making the game easy for me,” Horford said. “I just get to go out there and kind of be in the right spots and make the simple plays. I think he makes it easy for all us from what I’ve seen in the first couple of days.

“We’re still in the preseason, but honestly, I think Danny when he talked to me the first day I got up here in early September, he said to me: ‘Go out there and play your game and do what you’ve always done. Don’t worry about anything.’ I don’t feel any pressure, I guess. It feels right to be there. The more days that pass, the more comfortable I’m starting to get.”