Kristaps Porzingis had been a beacon of postgame optimism amid the roughest stretch of this Celtics season.

Boston, the big man repeatedly said, was close to rediscovering its winning formula after dealing with injuries up and down its lineup for the first two-plus months of the campaign. After a win in Denver last week, Porzingis confidently predicted the Celtics were “going to turn the corner and go on a nice run.”

He struck a very different tone after Wednesday night’s 110-97 loss in Toronto, oozing frustration as he addressed reporters in the Celtics locker room.

“I think we played with no spirit, with no personality,” Porzingis told reporters. “It was just a weak performance from us, honestly. We just play with no personality right now.”

The 10-31 Raptors are closer to the worst record in the NBA than to a playoff spot, and they lost to the Celtics by 54 points two weeks earlier. But they controlled play throughout Wednesday’s matchup, especially in the second half.

Down two at halftime, Boston allowed Toronto to shoot 73.7% from the floor in the third quarter, then scored just 15 points in the fourth. The Raptors led by double digits for the final 10:13.

“I think we individually have to look at ourselves, where we can improve, what we need to do better,” Porzingis told reporters. “Are we fit? Are we feeling good? Are we locked in mentally? And then try to fix some of the stuff that we have going on. But it’s not the end of the world. Every team has ups and downs. It’s just tonight, it feels like (expletive) right now, and we played some bad basketball.”

As for what went wrong in the fourth quarter — a problem period for the Celtics in several recent losses — Porzingis reiterated his initial critique.

“I thought we had no spirit, again, and we had no personality today as a team,” he told reporters. “We were just going up and down. It’s weird to say. We have high-character people here, but it’s just, things are not going our way. We’re a step slow here, there, this. Just no spirit, no personality.”

The loss dropped the defending champion Celtics to 7-7 over their last 14 games. They were unable to capitalize on a stretch of three straight matchups against middling-to-bad opponents, sandwiching double-digit losses to Sacramento and Toronto around a one-point home win over the New Orleans Pelicans, who missed a would-be game-winning layup at the buzzer.

Boston also had its full rotation healthy for all three games — a rarity this season.

“Even if I was panicking, if we were panicking, I would not tell you,” Porzingis told reporters. “We are not. We are not. But we are in a bad moment right now, for sure. We have to be realistic, look in the mirror. We are not playing the best basketball. We are not executing. We’re not doing this, this, this — it’s a lot of things that we’re not doing well, and we have to be honest with ourselves. Otherwise, we’ll just keep going like this … and then we’ll develop some bad habits.”

Porzingis’ performance Wednesday was one of the few bright spots for the Celtics. He shot 7-for-11 from the floor and 4-for-5 from 3-point range to finish with 18 points, eight rebounds, three assists, two blocks and one steal.

The 7-foot-2 center has made at least three 3-pointers in each of his last three games, shooting 52.4% from distance during that span. Payton Pritchard (20 points, 4-for-8 from three) also brought much-needed energy off Boston’s bench.

But the Celtics’ starting lineup has, bafflingly, been one of the NBA’s worst since Porzingis’ return from offseason leg surgery, and those struggles continued against Toronto. Every Boston starter finished the game with a negative plus/minus, ranging from Jayson Tatum’s minus-1 to Derrick White’s season-worst minus-29.

Tatum and co-star Jaylen Brown combined for a season-low 26 points on 31.0% shooting, with Brown going a dismal 3-for-14 on shots in the paint and 3-for-9 inside the restricted area.

Since Porzingis’ Nov. 25 season debut, the Celtics are just 5-5 when they have their preferred starting lineup available, and that group’s minus-11.8 net rating ranks second-to-last among the 33 NBA lineups with at least 130 minutes played.

“As a team, we’re still not clicking the way we need to,” Porzingis told reporters. “But in my opinion, it’s just a matter of time.”

The Celtics will need to make those improvements while they navigate a more challenging schedule. They’ll host the Orlando Magic and Atlanta Hawks — two teams to whom they’ve already lost this season — in a back-to-back Friday and Saturday night at TD Garden before hitting the road for their second Western Conference road trip of the new year. That trip features a visit to Golden State, a Los Angeles back-to-back against the Clippers and Lakers, and an NBA Finals rematch in Dallas.

“We just know that’s not who we are,” Porzingis told reporters. “So it’s in our hands to fix it.”

Slumping White

It’s hard not to wonder whether White is still feeling the effects of the illness that kept him out of last week’s win in Denver.

The veteran guard said he was “down bad” while he was battling that bug, and he hasn’t looked like the same player in the three games since, totaling as many turnovers (four) as made baskets (4-for-23, including 1-for-18 from three).

White had one of the worst statistical outings of his career Wednesday night (six points, one assist, no rebounds, blocks or steals in 21 minutes) and sat much of the fourth quarter in favor of Pritchard.

It was just the third time White, who entered the NBA in 2017, played 20-plus minutes and did not record a single rebound, assist or steal, and his first time doing so while also scoring fewer than 10 points.

“He’s just a guy that’s got to continue to play,” Celtics coach Joe Mazzulla told reporters in Toronto. “He’s been great for us the entire year. He’s just got to continue to play, continue to execute, continue to believe in himself. I believe in him. We love him. He’s going through a little slump, but he works hard enough. He’ll bounce back from it. Nothing really there.”

White also shot the ball poorly in the game before his illness, going 2-for-11 from three with three turnovers in a road loss to Oklahoma City. Before that, he’d been on a 3-point tear, going 14-for-25 from deep (56.0%) over his previous three contests.