In your wildest basketball dreams, what did the Celtics look like in these Finals?

Were they a whirring offensive machine that buried Dallas under hellacious rim attacks and a barrage of 3-pointers?

Did Jaylen Brown posterize three Mavericks with a single dunk in the first half? Did Derrick White, Al Horford and Kristaps Porzingis fire quick-trigger 3s and float back on defense, carried by the roar of the crowd?

What about their defense?

Obviously tied together on the proverbial string. Unspoken connectedness between five Celtics, switching and then blitzing and then sometimes dropping, all to keep Luka Doncic and Kyrie Irving into a perpetual state of unease. Boos raining on Kyrie.

Well for one half, your dreams, a city’s dreams, came true. All of them.

The Celtics reached a level, a flow state, unseen until Game 1 of the Finals on Thursday night. Given the stakes, the scene and competition, this was unequivocally the best basketball Boston has played all year.

It birthed a 29-point lead in the second quarter and five minutes of garbage-time celebration at the end.

This was the Celtics, finally, tested against a worthy opponent, under crunching pressure, freeing themselves from age-old frustrations and bad habits on basketball’s biggest stage. A fully engaged, focused group armed with an edge matching their unmatched talent. The Celtics who were promised.

Celtics 107, Mavericks 89.

One down, three to go.

Of course, being the Celtics, we did wake up for a stretch there in the third quarter. Doncic melted that 29-point lead down to eight, leaving TD Garden in an anxious murmur. But the Celtics did not melt with it; a meaningful show of grit for a group that dropped a Game 7 on its home floor last year and got out-toughed in the Finals two seasons ago.

With their lead at nine, Joe Mazzulla called timeout at 4:27 in the quarter, and the first-half Celtics returned. Brown forced his way to the line on the first possession, then Jayson Tatum hit a cutting Porzingis for an easy dunk after plucking an offensive rebound. Life sprung in the Garden again.

Then Irving, eager to silence a revived, spitfeul crowd, missed a 3 at the other end, and Brown burrowed back to the rim. Another foul drawn, more free throws.

Next Tatum hit a 3, and less than a minute later, with Irving driving, again eager to answer a Celtics bucket, Brown stuffed his ex-teammate at the rim. He flexed and snarled. Then Brown bellowed, eyes locked onto the crowd; a message sent.

Not here. Not now. Not tonight. The Celtics led by 15-plus the rest of the game.

Jaylen Brown of the Boston Celtics celebrates his 3-pointer during the second half of Game 1 of the NBA Finals at the TD Garden. (Photo By Matt Stone/Boston Herald)

While Thursday’s win was soaked in those kind of moments, it wasn’t revenge against Kyrie or the shot-making (38.1% from 3-point range) that defined their performance. It wasn’t even the stars — and we’ll get to Tatum in a second.

It was everything.

It was both sides of a team’s shared brain activated. Their reinforced backbone on display. Immaculate spacing, plenty of purpose and an attacking mindset on offense. A defensive fearlessness shaped and directed by a sharp game plan.

The Celtics held a Mavericks team that feasts on lob dunks and corner 3-pointers to zero lobs and one made corner 3. They turned Doncic, basketball possibility personified, into a single-minded scorer. He finished with one assist in a playoff game for the first time in his career and the first time all season.

Score one for coaching and Mazzulla. How about that?

It was a feisty bench lineup, led by Brown and Jrue Holiday, growing a 17-point lead against the Mavericks’ starters early in the second quarter. How? Sam Hauser splashed a 3, and this B-team unit not only survived Doncic isolations, but forced three misses from Irving before three minutes passed.

Then came Kristaps Porzingis; back from injury and playing with the spirit of late, great Bill Walton, who was honored pregame.

It felt like Porzingis simply couldn’t miss. He punished mismatches in the mid-post and canned open 3s. He collected three blocks in the final three minutes of the first quarter alone; pelts on his wall of defense that will be overcrowded by series end.

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Porzingis is a floor-spacing center, a problem the Mavericks, fully committed to protecting the paint, cannot solve without exposing themselves to mismatches. The Finals rest on his shoulders.

But let’s talk about Tatum. Guarding the Dallas’ centers, he will do a lot of dirty work that will go unappreciated, if not unnoticed, in these Finals. None of it will matter if he flings the ball around the court like he did Thursday with six turnovers and shoots 37% from the floor. The Celtics will risk this series, if not lose it, if he doesn’t bounce back.

But imagine a game where Tatum struggles like that, Doncic scores 30, and the Celtics cruise anyway.

Of course, there’s no need to imagine. No need to dream anymore.

It happened. The Finals are here. And the Celtics are three wins away from a title, at the peak of their powers with room still to grow.

Bring on Game 2.