Count Steve Kerr among those who didn’t expect the Celtics to be championship contenders this season.

Before Wednesday’s matchup at TD Garden, the Golden State Warriors head coach said he couldn’t believe how impressive Joe Mazzulla’s squad has been after losing a slew of key rotation players last offseason and playing its first 60-plus games without Jayson Tatum.

“The Celtics sure aren’t used to being an afterthought, and they kind of were before the season with Jayson’s injury and the departures of Kristaps (Porzingis) and Al (Horford),” Kerr said. “When we played them a month ago, I was just blown away by how good they were, the spacing, the execution. They just got good shots over and over again.

“They played so well together, and that was without Jayson even. I just think the continuity of what they’ve built has carried over so that, even with all the departures, they still know exactly who they are. And now they get Jayson back, of course.”

Porzingis, who started for Golden State in his first game back in Boston, said the Celtics’ rare turn as underdogs benefited them early this season. Kerr agreed.

“I think that time without the expectations really gave them a chance to play some of their younger guys, to kind of lay in the weeds a little bit,” the coach said. “Nobody was really talking a whole lot about them, and that’s kind of a nice position to be in if you’re used to being a favorite year after year. It feels to me like they really took advantage of it, developed some of the young guys, really hammered home their expectations for those guys and roles.

“I just thought every guy on that team knew exactly who they were, and so I’m just really, really impressed by the job Joe and Brad (Stevens) have done putting this team together. They’re a real, real favorite, for sure.”

The 46-23 Celtics dominated both of their games against the injury-depleted Warriors, winning 121-110 in San Francisco last month and 120-99 at home on Wednesday. Tatum and Jaylen Brown, who were reunited when Tatum returned from Achilles surgery on March 6, combined for 56 points in the latter.

“They put a lot of stress on you,” Kerr said. “To me, they’re the best spacing team in the league with all those great isolation players, (Payton) Pritchard included in that. When they start to drive, you really feel it when you play against them live. The guys on the opposite wing feel like they’re at half court. They’ve got multiple guys who can shoot from out there, but so many guys who can put the ball on the floor with obviously Jayson and Jaylen, but Derrick White is a great penetrator, and Pritchard.

“You’re so spaced out, so it’s really a matter of, are you willing to give up shots to certain players? You really have to know personnel. You have to be willing to give up certain shots to certain guys, but other guys, not so much. If you’re not in tune with recognizing personnel and you’re not in the right spot, they’re just going to kill you.”

Asked for his reaction to Kerr’s comments, Brown replied: “Yeah, it’s been fun.”

“You know, basketball is a team sport, so the strength of the team is what you lead with,” he said after Wednesday’s win. “And I think that from the beginning of the season, that’s what I’ve emphasized. And fast-forward to where we’re at now, I feel like we’ve improved at a very fast rate. And that does not happen in the NBA. Does not happen — a bunch of guys where you just plug and play and expect things to work out. Even though the expectation is high here in Boston, that just simply doesn’t happen in other places.

“But we’re very grateful, very blessed for our team to be able to be in the position we’re in now, and we’ve still got a lot of growth to do.”