The Celtics threw it back to Jan. 2003 on Tuesday night in Oklahoma City, and with apologies to J.R. Bremer and Vin Baker, that’s not a good thing, as the Celtics suffered their worst loss in 20 years by way of a 150-117 loss to the Thunder.

The 33-point margin of defeat was the franchise’s worst since a 52-point loss to the Pistons on Jan. 31, 2003.

“We got our ass kicked, that’s what happened,” Jaylen Brown said after the loss. “You come out and take it for granted, that’s what happens, and we probably had it coming us. Came out last couple of games [and] we pick and choose when we wanna play, we weren’t connected, didn’t have each other’s back out there, no help-side defense, we didn’t guard our yard.

“Those young boys over there [on Oklahoma City] came out and they made us look bad. They embarrassed us. They kicked our ass, and that’s what happened.”

Down by just one through the opening 12 minutes of action, things started to fall apart for Joe Mazzulla’s squad in a second quarter that saw the Thunder run the Celtics out of the gym by a 40-21 score.

The Celtics simply couldn’t get anything to fall in the quarter, with just five makes on 15 tries (and a 1-for-7 mark from deep), while the Thunder countered with a 16-of-25 shooting effort and four makes on 10 tries from deep.

The Thunder’s Isaiah Joe went off in the frame, with a Thunder-leading 17 points in the second frame behind a 6-for-9 shooting effort and three connections from beyond the arc.

Things didn’t get better in the third quarter — not even with what was a 27-point point quarter between Brown and Jayson Tatum — as the Thunder continue to drop absolutely everything into the bucket, this time with a 19-of-28 third-quarter performance headlined by eight three-point connections.

Oh, and the Celtics lost Marcus Smart to an ejection before the end of what was a nightmare third quarter.

Down by 31 after three quarters, the deficit was enough for Mazzulla to pull the plug on pushing in this contest, as he sat almost all of his starters for the entirety of the fourth quarter.

In a night full of stunning developments, the Thunder dropped 150 (their most points in any game since the franchise moved from Seattle to Oklahoma City) without Shai Gilgeous-Alexander available due to an illness. SGA entered the day as one of the league’s top scorers, averaging over 30 points per game this season.

The Thunder made up for his absence with efforts of 20-plus points from five different players, with Josh Giddey’s 25 points in 24 minutes leading the way for all OKC shooters.

For the Celtics, who are now within a half game of losing their hold on the No. 1 seed to the Brooklyn Nets, it was their eighth loss in their last 16 outings dating back to Dec 2.

But there’s no worry within the Green’s room just yet.

“I’m not concerned, but we have to coach in the short term and for the long term as well,” Mazzulla said of the loss. “It may not be the most popular thing to say but you gotta go through some shit if you wanna get to where you wanna get to whether it’s good or bad and that’s just how it is.

“We have to go though it, and we’ll be judged by how we handle it.”

The Celtics will see how they handle it with a Thursday night showdown with Luka Doncic and the Mavs.