Celtics

“We have to take responsibility,” Jayson Tatum said.

The Celtics were beaten by a division rival on Christmas Day in front of a national television audience.

It’s not like the Sixers (11-17) have been dominant this season. They have regained some of their glory, winning four of their last five games behind the stellar play of Tyrese Maxey, who has dropped 32 or more points in three of those contests.

There’s still a lot of basketball left, but if the season ended today, the Sixers wouldn’t even be in the play-in tournament. The efforts made by the defending champions on Christmas were unacceptable, as the players expressed in the post-match press conferences.

“We have to take responsibility,” Jayson Tatum said. “We have to acknowledge some things we’ve done that aren’t so great. We have to look in the mirror and behave. We just have to get better.

“We believe completely in ourselves and in the things we can do when we are completely locked down. We did this over and over again. We’ve had a few misses lately and we just need to get back on track.”

The Sixers were healthy, but the Celtics’ second loss of the week came on Monday against the Magic, who were missing three of their best players. With the loss on Christmas Day, the Celtics are now experiencing their first losing streak of the season.

The Celtics (40.8 percent) actually had an above-average shooting night from 3-point range. It was the little things that hurt them in this loss. They hit no free throws and shot 61.5 percent as a charity team. Philadelphia was a perfect 19-on-19 game.

It took too long for them to perform at both ends of the pitch and looked sluggish and not fully committed in the first half.

The fact that Kristaps Porzingis was limited to 13 minutes after suffering an ankle injury in the first quarter certainly didn’t help. The 7-foot-2 center tried to play through the pain but was clearly stymied for several minutes in the early going.

The Sixers took advantage by increasing the tempo, and the Celtics just didn’t seem ready to rise to the challenge. Jaylen Brown said the effort was lacking. Effort is the one thing you can always control, no matter what is happening around you.

“I just think we were too relaxed,” Brown said. “I just think we walked to our seats. Nobody was sprinting down the field, just hanging around and just trying to turn around to get the ball instead of just pushing it up the field and being aggressive. I feel like we started the game slow and they took advantage of that.”

The offensive rhythm just felt wrong, both Brown and coach Joe Mazzulla said. The Celtics were able to put Philadelphia under pressure defensively in the third quarter and only allowed 16 points.

Staying updated all evening is not a recipe for success.

“We play inconsistent basketball, so we have to be better on both ends of the court, be more consistent on both ends of the court,” Mazzulla said.

Thirty games into the season, the Celtics are still in pretty solid shape. They won 73 percent of their games. They are second in the Eastern Conference. They have dealt with a number of injuries that were not as common last season.

However, there were some differences compared to last year, which were particularly noticeable this week.

It’s a long season and there are nights like this, but they can’t be allowed to happen all the time. This is where commitment, discipline and coaching come into play. Games like this have to remain unusual if the Celtics want to keep Banner 19 flying.

“I think that’s a fair criticism from him,” Al Horford said of Mazzula’s comments about the inconsistent play. “I just think we need to dig a little deeper into our work to understand that we cannot relax during periods of play, no matter the circumstances. We need to make sure we are better in this regard.”

Khari A. Thompson

Sports reporter

Khari Thompson covers professional sports for Boston.com. Before joining the team in 2022, Khari covered college football for The Clarion Ledger in Jackson, Miss.