BOSTON — The Oklahoma City Thunder clinched a playoff berth Wednesday night.

But simply returning to the playoffs, after last year’s heart-breaking loss to the Dallas Mavericks in six games in the Western Conference semifinals, is far from the goal. Instead, the Thunder have their eyes on a far bigger prize: the franchise’s first NBA championship.

So, rather than the act of clinching that playoff berth, what mattered to Thunder guard — and NBA MVP frontrunner — Shai Gilgeous-Alexander was how they did it: by coming into TD Garden and beating the defending champion Boston Celtics on their home floor.

Doing so completed a sweep of the season series for Oklahoma City, and sent the loudest message yet about the intentions Gilgeous-Alexander and the rest of the Thunder have for the months ahead.

“It’s huge,” Gilgeous-Alexander said of the 118-112 win, after putting up 34 points, 5 rebounds and 7 assists in 39 minutes. “Because they’ve done it, because they’ve done what we’re trying to do, the games against them are always going to be heightened. They’re always going to be a little bit more exciting. They, like I said, achieved what we are trying to accomplish and there’s no better test in the NBA.

“You play for late June, and the other team had won late June. So playing against them is always fun, always a really big challenge and something that we get to test ourselves against them.

“I guess we passed two tests so far.”

Not only did the Thunder pass them with flying colors, but they won both games with key players sitting out. In January, it was Chet Holmgren who was watching in street clothes with a hip injury. Holmgren was back and starring for Oklahoma City on Wednesday night — putting up 23 points and 15 rebounds — while All-Star Jalen Williams was back home nursing a hip strain he suffered in Monday’s loss to Denver.

But Oklahoma City overcame both his and Alex Caruso‘s (illness) absences with a similar showing to the first meeting between these teams two months ago. In that contest, Boston couldn’t hit a shot in the second half, going 8-for-40 from the field and 3-for-24 from 3-point range.

In this game, the Celtics were red hot from 2-point range — they were 15-for-19 in the second half inside the arc, including a perfect 13-for-13 on shots in the paint — but were just 20-for-63 overall from 3-point range.

Those 63 attempted triples tied the third most in a game by any team in NBA history.

“I thought we got amazing looks,” Celtics coach Joe Mazzulla said. “I mean, that’s just the shell of their defense. They protect the paint first. They fight, they try to get out, their 2-on-1 reads were really good. So I thought we generated relatively great looks throughout most of the game.”

The numbers bear that out. According to Second Spectrum’s tracking data, Boston attempted 47 catch-and-shoot 3-pointers Wednesday — the Celtics’ second-most in a game in franchise history.

In the first half, Boston went 11-for-27 on those shots. In the second? The Celtics were just 4-for-20, finishing 21% below their expected field goal percentage on those shots.

For Oklahoma City, the irony of that was Monday against the Nuggets saw the Thunder shoot 20% over their expected field goal percentage from 3-point range, per ESPN Research — which is why coach Mark Daigneault said his message to his team while Boston got off to a hot start from 3 (9-for-22 in the first and 11-for-41 afterward) was to stick to the game plan.

“Our ability to just kind of stick with it and not overreact, not start to get jumpy … that’s when you really get in trouble against them,” Daigneault said. “So I just thought our maturity, our discipline to the game plan through the ups and downs of a tough 48-minute game was a really positive thing for us tonight.”

So was the play of Holmgren. With Williams out, there was a huge spotlight on the minutes Gilgeous-Alexander would be sitting, and how the Thunder would handle them. They did so by turning to their two-big lineup of Isaiah Hartenstein and Holmgren, and Oklahoma City wound up winning the nine minutes he sat out by three points, in large part due to Holmgren’s impressive showing, his highest-scoring game since returning from his hip injury last month.

“Chet was really good tonight,” Gilgeous-Alexander said. “He was impressive. We’re going to see him get more and more comfortable as the games go on, but he was special.

“He just played his game and he let the game come to him and that’s who Chet Holmgren is. That’s who he was before the injury.”

On the other side, Boston’s second star, Jaylen Brown, struggled mightily. While Jayson Tatum had an excellent game, going for 33 points, 8 rebounds and 8 assists, Brown never got going, finishing 5-for-15 — including 0-for-5 from 3 — before fouling out with more than three minutes remaining.

“You play for late June, and the other team had won late June. So playing against them is always fun, always a really big challenge and something that we get to test ourselves against them.”

Shai Gilgeous-Alexander

He credited Oklahoma City’s defense with completely taking him out of his rhythm.

“Tougher team sets the rules,” Brown said. “They had a good level of physicality tonight, and I could be more physical. I could use my body more, I settled in some spots, but I didn’t meet the level of physicality tonight. I had no free throw attempts, and that’s unusual.”

Boston found itself walking out of its arena Wednesday night knowing that if it faces Oklahoma City again in a few months in the NBA Finals, the Celtics will do so having been swept in the season series by the Thunder, and with poor second halves shooting the ball from the perimeter in both games playing a huge part in the result.

But Gilgeous-Alexander, when asked repeatedly about whether the Thunder were playing at a championship level right now, said there is a long way to go for Oklahoma City to get where it hopes to this season. And Tatum, for his part, isn’t concerned about where Boston sits, either.

“Everybody has to play a little bit better,” he said. “Better at the margins, the little things. You’re playing against contending teams that are not really gonna beat themselves. And the little things, make sure you get the 3-for-2, not fouling jump shooters at the end of the clock, live-ball turnovers, things like that, you just gotta be a little bit better on.

“We all do. And we will.”