At the next stoppage, Hauser was replaced by Jaylen Brown.

Maxey felt it was disrespectful for Hauser to guard him one-on-one, and that’s what the All-Star guard should have done. The Celtics never fully recovered from that upset as they lost again on Wednesday, 118-114, to the 76ers, who are playing six games under .500.

The Celtics were deadly in December, losing five of 11 games with a defense that plays hard when it feels like it. Not only did Maxey score 33 points for the Celtics, Caleb Martin (remember him?) added seven 3-pointers but continued to stay open.

Now the Celtics will say that this was the game plan, that they will substitute Maxey with hard-fought twos, and that they will give Martin, who made just 18 3-pointers in 22 previous games this season, the free shot because he had problems.

But there comes a point when conventional wisdom, playing with percentages and relying on the law of averages must be discarded when the same things keep happening. Martin hit four of his seven 3-pointers in the fourth quarter as the Celtics remained adamant that he would cool off.

“That was the game plan; We stick to the game plan,” Brown said. “We trusted the game plan. Martin shot seven threes and that’s tough and he’s done that to us in the past. But once we got into it, we felt comfortable letting him take all the shots and he just knocked them down tonight.”

The 76ers were one of the league’s bigger disappointments. Joel Embiid missed 19 games and barely played with Maxey and Paul George. But this was their best performance of the season and the sleepy, almost disrespectful Celtics were caught off guard, just as they were Monday in Orlando when they lost to the Magic without three of their top four scorers.

The Celtics aren’t going to assert themselves as champions by shooting a ton of threes and playing porous defense. This is the team they are now.

“We were inconsistent,” Mazzulla said. “In this game it was the discrepancy with our performance. We play inconsistent basketball. We have to be better on both ends of the court.”

The Celtics lost on a night when their starters combined to make 20 3-pointers because they couldn’t get defensive stops. They were overwhelmed and the 76ers blew up the scouting report by shooting much better than expected. Embiid shot 21.2 percent from the 3-point line but made 4 of 5.

Opposing teams are no longer intimidated by the Celtics’ 3-point barrage. They destroy their defense, overwhelm them on 50-50 balls and cause ball losses. The Celtics started Christmas Day like they had too much eggnog, committing six turnovers in the first quarter in a game they were never in control of.

“We were just too relaxed,” Brown said. “I think we walked to our seats. No one was sprinting across the floor, just hanging around and just trying to turn around to get the ball instead of just pushing it up the field and just being aggressive. We just couldn’t get a full 48 (minutes) together. I’m not really sure why. It felt kind of strange. As a group we have to get better.”

Jayson Tatum has enjoyed many moments of being the best player on the field as he leads the Celtics as they overwhelm their opponents with their accurate 3-point shooting and cohesive defense. And he recognizes that the Celtics have lost some of their self-confidence.

They have more home defeats (five) than in all of last season (four). Opponents are better prepared, employing different game plans and nullifying Boston’s weak interior defense. The Celtics responded with three-pointers and brave rallies late in the game, but they weren’t enough.

“We’ve always emphasized being a really, really good defensive team that takes pride in running the ball, and we need to get back to that,” Tatum said. “We have to take responsibility and acknowledge the things we didn’t do so great. We have to look in the mirror and behave. We believe fully in ourselves and in the things we can do when we are completely locked down. We did this over and over again. We’ve just had some mistakes lately.”

Before the season, Mazzulla promised that his team would not view this season as a chance to repeat, but as a chance to pursue the same goal as the other 29 teams. They wanted to put the 2024 championship run aside and play with the same passion and determination as last season, when they were simply competitors.

But after a strong first six weeks of the season, the Celtics have faded. They don’t play with the same intensity. They have lost their self-confidence. They handle the ball carelessly, shoot three-pointers, miss defensive tasks and miss free throws. And the rest of the league is happy about their relegation.

“We’ve been to three conference finals in a row, two finals appearances in the last three years,” Tatum said. “We have always had the best results in the last three years, so this shouldn’t surprise us or anything like that. It should be something that is expected. I keep saying it. “We have to get back to ourselves, our identity. We haven’t shown that in the last few games and we have to get ourselves together again.”

Gary Washburn is a Globe columnist. He can be reached at [email protected]. Follow him @GwashburnGlobe.