Continuity was supposed to be one of the 2024-25 Celtics’ greatest strengths. Instead, it’s been one of their biggest concerns as they near the season’s halfway point.

Though Boston returned its entire core rotation from last year’s NBA championship team, a steady drumbeat of injuries has forced it to play shorthanded in nearly every game thus far.

Sunday’s matchup with the New Orleans Pelicans at TD Garden marked just the fourth time this season that head coach Joe Mazzulla had all of his rotation players available at tipoff, and just the ninth time he had his preferred starting five of Derrick White, Jrue Holiday, Jaylen Brown, Jayson Tatum and Kristaps Porzingis intact.

That starting lineup should be one of the most dangerous in the NBA, but it’s struggled in its limited floor time together this season.

Entering Sunday, those five players had logged just 116 total minutes together through 39 games, and the Celtics had been outscored by 10.3 points per 100 possessions with that unit on the court. Boston also came in with a 4-4 record in games that group started (23-7 in all other contests).

Last season, the White-Holiday-Brown-Tatum-Porzingis quintet played 623 minutes together — twice as many as any other Celtics lineup — and outscored opponents by 11.3 points per 100 possessions.

“It takes continuity,” Mazzulla said. “What’s (Porzingis) been back (since his latest injury), three games? Four? So I think his wind’s getting back. But really to me, it’s not even a physical thing. It’s more of tactical stuff of our guys getting reps with each other, our guys getting reps as a team. I think to this point, I was looking at it earlier, and we’ve played 115 minutes with our starting five, and last year, it was, like, triple that.

“So it’s not as much the physical as it is the rhythm and the trust and the habits that we have to build, whether it’s breaking to your spots on the offensive end, having the recognition of what the matchups are, making sure we’re executing versus the right coverage, making sure defensively we’re in the right positions and communicating the proper way. … It’s just continuing to build trust and habits amongst the guys.”

Mazzulla said during the Celtics’ recent four-game road trip that the starters had just reached the number of reps they typically get together by the end of training camp. Porzingis’ absence has been a significant factor in that — he missed all of camp and the — but Boston’s other big names also have been dinged up.

Every starter has missed multiple games: two for White, three for Tatum, six for Holiday, seven for Brown, 23 for Porzingis and nine for pseudo-starter Al Horford, who typically gets the call when any of the top five can’t go.

Even though those players all played together last season — as did bench regulars Payton Pritchard, Sam Hauser and Luke Kornet — Mazzulla said the frequent lineup shuffling has disrupted their rhythm, contributing to Boston’s inconsistency. The Celtics entered Sunday with an 8-7 record over their previous 15 games, already have lost more home games than they did all of last season, and trailed the first-place Cleveland Cavaliers by 6.5 games in the Eastern Conference standings.

“You can’t overestimate the importance of details, habits and execution,” Mazzulla said. “So we just have to continue to work that, hold each other accountable to it, rep it, demand it from each other. That just comes with a little bit of time, and the most simplest things to do are the hardest things to do, so we’ve just got to continue to do it (and) work at it.”

Health report

The only Celtics players who were unavailable Sunday were their four G Leaguers. Two-way players JD Davison and Anton Watson and first-round rookie Baylor Scheierman were on assignment with Maine, and Drew Peterson missed his second straight game with a concussion.

Mazzulla said Peterson, who’s appeared in 11 games for the big club this season, was progressing well.

“He’s getting better,” the coach said. “He’s doing good. He was out on the floor a little bit (Saturday), just shooting a little bit, some non-contact stuff. So he’s getting better.”

Reserve forward Jordan Walsh was active after sitting out the previous two games with an illness.

New Orleans was down starters Brandon Ingram (ankle) and Herb Jones (shoulder) but got franchise centerpiece Zion Williamson back from the one-game suspension he received for arriving late to a team flight.

Availability has been an issue throughout the season for the 2019 first overall pick. Sunday’s game was just Williamson’s eighth of the season.

Pelicans head coach Willie Green said Williamson needs to “maximize the number of games that’s in front of him.”

“He’s a force when he’s on the floor, so keeping him healthy will be important,” Green said.

Springer’s niche role

Guard Jaden Springer has spent most of the season buried at the bottom of Boston’s depth chart, but he’s seen fleeting moments of meaningful action in a few recent games.

Mazzulla occasionally has inserted Springer, whose defense is far more developed than his skills on the offensive end, on opponents’ free throws and inbounds plays in the final seconds of quarters. His assignment: make sure the other team doesn’t pull a Pritchard.

“There’s times where I’ll put Jaden Springer in with, like, 0.5 seconds left or one second because of his ability to guard full-court in those situations where a T.J. McConnell or a Payton can’t get there,” Mazzulla said. “There was a game last week where somebody hit a half-court shot because (the other team) didn’t execute it in a great way. I showed Jaden and I said, ‘This 1.5 seconds is just as important as if you went in at the start of the second quarter.’”

Mazzulla said how deep bench players handle the opportunities they do get, however infrequent those are, influences whether they’ll see more playing time in the future.

Springer’s future with Boston is uncertain, as he’s the Celtics’ most logical trade candidate ahead of the NBA’s Feb. 6 deadline.

Off the rim

Green played with Al Horford in Atlanta during the 2011-12 season. He called the veteran Celtics big man “one of my favorite teammates of all time, one of my favorite people of all time.”

“He’s a pro’s pro,” Green said. “I think everywhere he’s gone, people sing his praises. They speak highly of him. He’s a high-character, hard worker, and there’s a reason that you get a guy like Al on this team, and they’re having success because not just the talent, but the character that he brings into this building.” The 38-year-old Horford is in his 18th NBA season.