Celtics guard Derrick White passes the ball from the floor while Pacers center Myles Turner tries to knock it away during Boston’s 117-112 loss on Wednesday at TD Garden. Charles Krupa/Associated Press

Two weeks ago, the Celtics were 21-5 and looked like they were a tier above the rest of the NBA. Since, Boston is one miraculous late-game comeback away from a six-game losing streak.

Boston hit a new low in the first half of its 117-112 loss to the Pacers on Wednesday night in Boston. The Celtics fell behind by as many 30 after a listless first-half performance. They rallied to make things interesting in the fourth quarter but the deficit was too much to overcome.

Heavy boos from the Garden crowd were heard for the first time this season. Coming off two straight losses at home to the Orlando Magic, Jayson Tatum said he thought the harsh treatment was deserved.

“We got booed, you never want to do that,” Tatum said. “Rightfully so. But it’s all about how we bounce back. There’s literally nothing we can do right now to change what happened. So you gotta get ready for the next one.”

Tatum did his part, bouncing back from a rough first half to score a game-high 41 points. However, his running mates remain stuck in a malaise.

Jaylen Brown (8 of 23, four turnovers) had another inefficient performance with plenty of defensive miscues. Derrick White has missed his last 12 shots from beyond the arc. Malcolm Brogdon (5 of 13) struggled to finish against his old teammates. Offensive woes carried over to the defensive end of the court, and that’s cause for concern according to Tatum.

“We just gotta regroup,” Tatum said. “We gotta get back to – we gotta learn how to win again. I think it’s not as simple as that, but we gotta get back to having fun. I think we’re playing a little timid, a little tight. Basketball is supposed to be fun, it’s supposed to be loose, it’s supposed to be competitive. But I get a sense of, like, everybody wants to make every shot, myself included.

“Our body language when we miss shots and things like that is contagious. And that’s just part of it. We’re not going to make every shot, we’re going to turn the ball over, it’s all about how we respond. And as a group, we can’t let it snowball. And that’s what happened tonight. We let it — it’s a domino effect. I think just not playing so tight, get back to just relax, take a deep breath, and remember we’re playing basketball.”

Interim coach Joe Mazzulla laid it out in simpler terms after seeing his team outscore the Pacers by 23 points in the second half before falling short.

“I’m not really concerned about (the effort) in the sense of it’s the first that we’ve had where we really were outplayed from an effort standpoint,” he said. “That would be more concerning if we didn’t play a completely different style in the second half. We just have a choice to make: what team do we want to be? The team we were in the first half or the second half.”

The Celtics still have four games left on their season-long seven-game homestand, including a Christmas Day tilt against the Bucks. From a big picture standpoint, Boston would have taken a 22-10 record to begin the year, but it doesn’t feel nearly has promising after seeing a team drop five of their last six. As old habits and poor body language pop up, Tatum believes the antidote Is simple for this group.

“I think we just need a win,” Tatum said. “We have fun together off the court. We bond. This is a close group. We’re just having a tough stretch. We’ve had a tough stretch every year since I’ve been in the NBA and this is no different. We gotta figure it out. We gotta regroup. We gotta get back on track, essentially.”

MARCUS SMART is questionable for Friday’s game against the Timberwolves as he continues to battle a non-COVID illness according to the Celtics injury report. Smart missed Wednesday’s game against the Pacers due to sickness as Boston struggled yet again to their third consecutive home loss to the Pacers after an atrocious defensive first half. Danilo Gallinari was the only other Celtics player on Friday’s injury report as he continues to recover from a torn ACL.

With Smart out of the lineup, Payton Pritchard drew a surprise start in Wednesday’s matchup against the Pacers alongside Derrick White but he made a limited impact with just three points and four assists in 17 minutes.