SAN FRANCISCO — Klay Thompson left the Warriors with a whimper.

He returned to the Bay with a roar.

Nothing less was expected. Nothing less would have been appropriate.

Tuesday’s game was circled on the calendar the moment the schedule was released, and not because it was the first game of the NBA’s in-season tournament. No, this was an opportunity for a grateful organization and adoring fan base to celebrate one of the greatest ever to wear “Golden State” across their chest, to say thank you for four banners and countless memories.

Jerry Seinfeld once joked that sports is little more than rooting for laundry. It’s a good joke, but, obviously, sports are so much more than that.

We all have a basic need for belonging, for community. It’s built into our DNA. And sports can fulfill that need.

Countries and even families can be divided, but we can all come together under the banner of the local team to enjoy something as frivolous as a game.

And the athletes who demand our collective attention — the ones who give us something to cheer about — are unforgettable.

Even if he parted under less-than-ideal circumstances — a contentious season capped by an 0-for-10 performance in the Warriors’ one postseason game, followed by unceremonious exit to Dallas in free agency — Thompson will forever be in that legend category around these parts.

That’s why he was given a guard of honor from Dubs employees when he entered the building on Tuesday. That’s why the whole arena gladly wore the team’s gate giveaway, a white captain’s hat. That’s why Thompson was given a long, raucous standing ovation before the game started and was cheered when he made two free throws to open the game.

“I was a little misty-eyed, for sure,” Steve Kerr said.

“It was really cool to see the fans’ gratitude,” Thompson said. “That’s something I’ll never take for granted.”

We all had grown used to not seeing Thompson in a Warriors uniform. He missed two-and-a-half years due to injury, after all.

But yes, it was weird to see him wearing different laundry.

And, absolutely, it was all a bit awkward celebrating someone who was actively going against Golden State.

Thompson can attest to all of that himself.

He couldn’t hide his body language during the seemingly endless cheers for him pregame. Given where Thompson is in his career — a lesser version of the all-time-great he once was, Tuesday had to feel like he was attending his own wake.

And you can’t blame Thompson, after making his third 3-pointer of the game halfway through the second quarter, for running to the opposite side of the court as the whistle blew for a timeout. It was muscle memory — that’s how he would celebrate with Dubs fans in the past. He caught himself, realizing that he does not, in fact, live here anymore.

Amid all that adulation and peculiarity, there was catharsis as well.

Thompson played well on Tuesday, scoring 22 points on 7-of-17 shooting, with all but one made basket coming from behind the 3-point arc.

But the Warriors are playing well without Thompson. And you’d be hard-pressed to argue that they’d be better off with No. 11, seeing as Dubs general manager Mike Dunleavy turned him into Kyle Anderson and Buddy Hield via an elaborate sign-and-trade this July. Anderson was a late scratch with neck spasms on Tuesday, and Hield had an underwhelming game, but De’Anthony Melton, whose free-agency addition was made possible by Thompson’s exit, was immense next to Steph Curry in the starting lineup. All three have been outstanding to start the season.

Somewhere after that third Thompson 3-pointer and the accidental celebration, the night’s pomp and circumstance faded, and the game took center stage. And it was a hell of a game, too. That Steph Curry guy (37 points, a night-night 3-pointer with 26 seconds remaining) has a bright future in this league.

“It hurts to be on the other side of one of his flurries,” Thompson said amid a press conference where he had to refer to Curry and the Warriors as “them” and “those guys.”

“When you play someone you’re close with, you want to beat them even more,” Draymond Green said after the game. “It just raises that level of competition.”

One could have even inferred that Curry was angry at Thompson, given how emphatic his celebrations were following his big 3-pointer. He yelled something like, “You miss it here?” into the TV cameras, pointing to the floor and the Golden State on his jersey. You can forgive Curry if he forgot to be politically correct at that moment. He ran the proper lines after the game but said he “forgot” what he said to the camera.

“It’ll always be weird” to play Thompson, Curry said. “There’s nothing that can cure that. You’ve heard us talk for years about all wanting to finish with one organization.”

Alas, that’s not how it all went down. And with this game — and all the emotions that surrounded it — in the books, everyone can now move forward.

After the game, Thompson stood in the middle of the court, hugging Warriors staffers and players.

And as he exited, he received another loud ovation from Warriors fans.

Thompson tried to downplay the emotions of his return in the lead-up to the game. He certainly wasn’t happy his team lost, especially after holding a late fourth-quarter lead.

But as Warriors fans chanted his name on his way down the tunnel, he couldn’t help but smirk.

It’s good to be home, even if only for a night.