SACRAMENTO, Calif. — The Celtics are turning into Motown Records in the late 1980s, living off the name and the reputation, but no longer producing those million-sellers.

The Celtics are no longer those formidable opponents who would step into opposing arena and win with skill, experience, and precision. Each game has turned into an embarrassment and this three-game road swing out West exposed them as perhaps a playoff pretender.

It wasn’t the streaking Clippers or upstart Warriors who applied licks and uppercuts to their inferior opponent from Boston, it was the 11-19 Sacramento Kings, one of the league’s downtrodden teams, who pounded the Celtics with relative ease, humiliating the Celtics, 118-96, on Sunday at Sleep Train Arena.

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Sacramento hit seven 3-pointers in the fourth quarter as the Celtics’ defense simply relented, refusing to run out to open shooters, allowing the Kings to set their feet and launch long-range shots as if it was a Sunday afternoon at the carnival.

On this three-game California swing, the Celtics allowed an average of 108.3 points and trailed after each quarter. The Kings turned a 2-point third-quarter lead into 11 by the end of the period and then stomped on the Celtics’ pride with a ridiculous fourth quarter in which they made 12 of 19 shots.

A team that once considered defense its identity is now allowing players such as Isaiah Thomas, John Salmons, and Jason Thompson to carve it up with little resistance.

“Defensively, we were bad the whole trip,” Celtics coach Doc Rivers said. “We’ve just got to do better. I’ve got to figure out the right guys to do it consistently every night. Every time we look like we’re going to make a run, we give up a layup, [3-pointers]. Tonight, we just had breakdowns, so it’s disappointing.”

On a night when he was 4-for-12 shooting, much-maligned DeMarcus Cousins collected his first NBA triple-double with 12 points, 10 rebounds, and 10 assists, but he wasn’t the story. Thomas, the 5-foot-8-inch second-year guard, outclassed counterpart Rajon Rondo, scoring 27 points on 10-for-15 shooting. Rondo, who returned to the lineup after missing Saturday’s game with a bruised hip, scored 2 points on 1-of-6 shooting.

A team that averages 96.8 points per game scored 94 in the final three quarters tried to be kind afterward.

“I don’t know, maybe it might have been a back-to-back [games],” Thomas said when asked about the scoring ease. “They are old, but they’re definitely one of the best teams in the NBA and we just had their number today.”

Paul Pierce and Jason Terry led the Celtics with 20 points each while Kevin Garnett and Jeff Green added 16 apiece. But those efforts were hollow. The Celtics were rendered helpless on defense, unable to close out to open shooters, allowing numerous dribble drives or fouling instead of forcing a tough shot.

The players have said repeatedly that the execution has to be more consistent but no progress is being made. With two days off before Wednesday’s matchup with the Memphis Grizzlies, the Celtics are clueless as to their identity.

“We’ve got to play better than that,” Garnett said. “We all gotta have some pride in ourselves, man. We gave up 100-something points three games in a row, not even being close. We gotta at some point take it personal, you know? It’s not all on the coaches, it’s on players.”

Garnett said the players have to be held accountable.

“Yeah because we built something here,” he said. “I’m not living in the past or nothing but the reason why guys came back [to the Celtics] and made a commitment to this team because of what we [established] that we’ve been known to defend. We’ve gotten away from that so we have to go back to our origins to figure it out.

“We’ve got to find some self pride in here. I don’t know what we are right now.”

Behind the scoring of Terry and Green, the Celtics made a second-quarter charge, actually leading, 35-31, after a long 3-pointer by Terry capped a 17-7 run. But prosperity didn’t last but mere minutes as the Kings responded with a 13-3 surge to take a lead they would never relinquish.

The Celtics couldn’t stop the Kings in transition or in the paint, allowing players such as Salmons and Thomas to repeatedly take defenders off the dribble. Boston reduced the deficit to 50-47 after a Green dunk, but Salmons responded with a streaking layup and Cousins, who could be on the trade block, slammed home a baseball pass with 1.5 seconds left.

Garnett salvaged the quarter with a layup of his own at the buzzer, but the Celtics would lose control of the game early in the second half.

The Celtics have now dropped seven of nine games and allowed 100 or more points in 11 of their 16 losses. The defensive mind-set is decaying and even the veterans are unsure how to resurrect their reputation.

“We’re a defensive team, we just gotta do it,” Garnett said. “I know we’re not showing up as far as stats and what we’re doing in games but we’re a defensive team. Don’t get that twisted. We’re just not defending right now. As long as Doc’s here, that’s what we’ll always be.”