Well, that was something.

What it was was a massacre. A beating. A blow. It was a spanking and a beating. It was a beating and an assault, a massacre and a bludgeoning. It was certainly an eye-opener and stomach-churning when your loyalties were with the team wearing white uniforms instead of those wearing green uniforms.

What it was was Celtics 132, Knicks 109, in Boston’s TD Garden, and it could easily have been much, much worse if the Knicks hadn’t waved a white flag that the Celtics accepted, but only after they were in the Knicks’ eyes had poked. a few more times. This was like a college buying game, with the Knicks taking $500 to hand over their heads on Homecoming Day.

The Celtics raised a banner and then laid down a gavel.

“We have to be a lot better defensively than we were before,” Knicks coach Tom Thibodeau said when the carnage was complete. “There was some indecision. When you play against a team like that, you have to scramble. One attempt is not enough, you have to make a second, third and fourth attempt. And even then, they still have the ability to make something.”

They do. At one notable point in the second half, the Knicks shot 59.1 percent from the field, the C’s 58; the Celtics led 99-70.

No, this wasn’t the way Thibs hoped this would go. This certainly wasn’t what Leon Rose had in mind when he drafted the roster for the express purpose of being a better fit for the Celtics. As opening nights go, this was “Moose Murders,” and if you’re not an expert on Broadway trivia, you can trust me or Google it. This was so bad.

And also conjured up the famous final scene of “The Candidate,” with Robert Redford’s Senator-elect Bill McKay pulling Peter Boyle’s Marvin Lucas into a hotel room and asking, “What do we do now?”

Well, at least Thibodeau managed to collect more teaching moments in these 48 minutes than in the entire preseason. Look: The Celtics are currently the NBA’s gold standard. They are the defending champions, and as complete and intact as a champion has been since the 2004-05 Pistons, even without Kristaps Porzingis.

The Knicks? In comparison, they are still getting to know each other. They’re still in the bonding phase, and Tuesday night’s study in team building was watching them combine to make 29 of the Celtics’ first 48 3-pointers. Some of them were open. Most were controversial. And with each photo, you could see the light in the Knicks’ eyes fading.

(It was almost hilarious that the moment the Celtics tied the NBA record with that 29th 3 — with just under nine minutes to play — they missed their final 13 shots of the game, and while the crowd begged for another chance at the record on their last possession, Boston coach Joe Mazzulla ordered them to take a knee instead. Like I said: ALMOST hilarious.)

“The NBA needs to drug test these guys,” Josh Hart said, joking after it was over because what else can you say? “I’ve never seen anything like this before.”

So this is where you start: you look for the thin reed of positivity that has grown up through the mud and muck. Deuce McBride, for example, scored 22 off the bench on 8-for-10, just as we remember him from last spring’s best nights. Limited to just 24 minutes after the game got out of hand, Karl-Anthony Towns showed why he will be fun to watch all year long.

Perhaps the most important was Mikal Bridges’ second half. Bridges had been brutal across the board in the first half, missing all five of his shots and looking like a putter with a bad yips when he strained his arm to shoot. But in the second, he went 7-for-8 and 2-for-3 from 3. The game was already decided, but that came against the Celtics starters. It was something.

It’s a long season, yes. It will be a long time before the critical hours of April, May and June arrive. It only counts for one loss, exactly the same as a four-overtime gut punch would: indisputable.

But also a bit worrying. How could it not? The Knicks believed they had at least made progress in closing the gap with the Celtics. And they can still do that. But for now, after one game, a game where they wanted to see where they could measure up to the Celtics, the result was a painful diagnosis everywhere: head, heart, eyes, ears, esophagus.

It was a long night. Luckily for the Knicks, it’s also a long season.