“We were dealing with some ups and downs,” Irving acknowledged, after scoring 26 points with 11 assists and seven rebounds. “But I think we have an appreciation for the group that we have. We’ve spent at least two years together now. Everyone’s healthy other than Smarty [Marcus Smart, left oblique tear]. So I think we have a good rhythm of the expectations for each other.”

Irving played with his pedigree showing in the opener, making tough shots while setting up other Celtics to keep their squad safely ahead after the second quarter.

Somehow, then, Milwaukee point guard Eric Bledsoe wound up with a nightmarish afternoon: A nemesis from last spring’s first round showdown, Boston guard Terry Rozier, outplayed him again. And Rozier did it off the bench, because Irving’s dominance came as the Celtics’ starter (after missing the 2018 playoffs entirely).

Horford, meanwhile, seemed to step out of the wayback machine, putting up prime numbers (20 points, 11 rebounds, three blocked shots) just five weeks shy of his 33rd birthday. He and Irving clicked time and again on pick and rolls.

Al Horford stuffed Giannis Antetokounmpo time and again on Sunday.

And Horford was even better on defense, as the primary defender against Antetokounmpo in a sagging defensive scheme that brought a lot of help to the Bucks’ MVP candidate. One for all, all for one, and the Celtics turned Antetokounmpo’s personal playground (the paint) into a no-fly zone. "The Greek Freak" made his biggest mark by hitting 3-of-5 3-pointers; otherwise, Antetokounmpo shot 4-of-16 and earned his minus-24 for the game with a quarter to spare.

It makes a little more sense that Horford didn’t sweat the regular season. Boston’s coaches and medical staff kept him on a short leash of wear ‘n’ tear, precisely so he would be strong and available for performances such as this.

“For me, everything is heightened so much [in the playoffs],” Horford said. “The intensity of the fans … I just think the focus level goes way up. For our group, that was something [we] had a hard time with in the regular season.

“Once the postseason started, we all really [bought in]. Kyrie has been in our ear even weeks before the regular season ended … about how we need to prepare and be better. I think all the guys understood what he was trying to tell us and took him up on that challenge.”

Celtics coach Brad Stevens claimed to notice improvement in the closing days of the regular schedule. Last week, Stevens even cited a home game in late March against the Pacers in which he saw the Celtics finally jelling. “Intentional play and purposeful details,” Stevens called it.

What will matter most in Game 2 of the East semis?

That stuff was everywhere Sunday, along with determined party-pooping for a sellout crowd at Fiserv Forum that anticipated so much more. Milwaukee was outrebounded and outscored in the paint, and led for only 58 seconds of the game’s final 44 minutes. They shot 34.8 percent, including 10-for-34 on 3-pointers by all those perimeter players employed expressly to pull defenders away from Antetokounmpo.

Stevens started Marcus Morris, brought Aron Baynes off the bench and got strong play from Rozier and Gordon Hayward in reserve. Eventually, the Celtics will have to make room for Smart, too, if this series or their postseason runs long enough. With things so currently copacetic, that shouldn’t ruffle anyone.

Getting off to a good start in the series was considered to be vital for Boston to avoid possibly splintering or squabbling. But as it turns out, the Celtics aren’t doing that stuff anymore and that’s what fueled the Game 1 blowout.

They blithely talked all season about flipping the proverbial switch when they hit the playoffs. And now, they appear to have done it.

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Steve Aschburner has written about the NBA since 1980. You can e-mail him here, find his archive here and follow him on Twitter.

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