Boston Celtics interim head coach Joe Mazzulla insists he is not concerned about his side's form despite slumping to their fifth loss from six games in Wednesday's 117-112 loss to the Indiana Pacers.

The Celtics were blown away 71-43 in the first half against the Pacers, eventually falling to their third straight loss despite a second-half rally led by Jayson Tatum with 41 points.

"I'm really not concerned about that, in the sense that I think it's the first half that we really got outplayed from an effort standpoint," Mazzulla told reporters.

"It 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 from the first half or the team from the second half?"

The result means Boston slip to a 22-10 record overall, sitting second in the Eastern Conference behind the Milwaukee Bucks (22-9), who also lost on Wednesday to the third-placed Cleveland Cavaliers (22-11).

"I don't really get concerned," Mazzulla said. "We are where we are. You have to rely on who our guys as people and the process of what we're trying to build.

"We're not playing well. Up until this point we have competed defensively and it was an offensive issue. In moments like this it's important to trust your guys. Because they've been through a lot, they've had moments like this, they've had bounce back.

"We're going through a hard stage but that's part of the NBA. It's also hard when you play the way you did at the beginning of the year and at such a high standard. We need to learn to set that standard as a habit."

The Celtics closed several times in the final quarter but Mazzulla rued their start, particularly the first quarter where the Pacers piled on 42 points.

"We just didn't play with a great sense of urgency, didn't play with awareness and didn't play with a sense of details," Mazzulla said.