INDIANAPOLIS — The Celtics perhaps saved face and their reputation in the fourth quarter Wednesday night with a dramatic comeback from a 24-point deficit to force the Pacers into overtime.
Before the 9-minute mark of the final period, the Celtics were playing their worst game of the young season. They were a step slow defensively, couldn’t make a layup and neither Jayson Tatum nor Jaylen Brown could score consistently.
The Celtics are good enough to camouflage many of their weaknesses with a stellar stretch. They outscored the Pacers by 21 points, behind Tatum’s rejuvenation, to turn a clunker into a thriller. But that comeback proved futile as Pascal Siakam drained a top-of-the-key 3-pointer with 6.1 seconds left in the Pacers’ 135-132 Pacers win at Gainbridge Fieldhouse. It knocked the Celtics from the ranks of the undefeated and magnified their early-season issues.
Their overall talent is good enough to win every night, and there will be rare occasions this season in which the Celtics won’t be favored. But Tatum and Brown attributed Boston’s 24-point deficit in the third quarter to a lack of energy.
They certainly didn’t lack energy in Monday’s 119-108 win over the Bucks. But there are going to be nights during the grueling NBA season where the legs are heavy, where the opposing team has more motivation, especially the Pacers, who have become a recent rival and entered with three consecutive losses.
Perhaps Indiana wanted it more Wednesday. And there are going to be nights where the desire lacks. But the Celtics can’t be fooled by their ability to rally, to play 10 brilliant minutes and turn the Pacers into a bumbling bunch in the final minutes.
Tatum and Brown were a combined 6 for 29 from the 3-point line and neither were good, except in some clutch moments. The Celtics deserved to lose because they were outplayed and outhustled, and those nights will happen.
The good news is each took accountability for their efforts.
“I just really didn’t like the way I started the game,” Tatum said. “I set the tone in a negative way and my energy wasn’t where it needed to be and I just felt like that had a domino effect. We were a step behind on offense, on defense, so I take a lot of the blame for that. I just wanted to pick it up in the second half.”
The Celtics have heard how good they are for weeks now. And they have played like it mostly, a dominant opener against the Knicks, an easy win against the Wizards. But they needed a late comeback to eke a win at Detroit and then a dominant fourth quarter to overcome the Bucks.
They never had any grip against the Pacers, who behind Bennedict Mathurin and Siakam, led for 2½ consecutive quarters before Tatum tied the game with a 3-pointer with 14.4 left in regulation. The Pacers got every loose ball, every key offensive rebound while the Celtics bobbled numerous chances to rally.
On their final offensive possession, Brown airballed a potential tying 3-pointer with 5.3 seconds left. It was a fitting end to a difficult night for Brown, who dominated the Eastern Conference finals series against Indiana just five months ago.
“Our energy was lackluster and a lot of that is on me,” Brown said. “I have to be better for my guys. Just converting at the rim, simple stuff, making open shots. We put ourselves in a hole early in the game, just not converting open looks, not being physical enough on drives, finishing at the rim and a lot of that is on me. But way to battle back. We had an opportunity to win.”
The sign of a great team is never relenting, even when it has every reason to. Celtics coach Joe Mazzulla, who lives proudly in the unconventional, decided to stick with his starters along with reserve center Neemias Queta when the Celtics appeared cooked in the final nine minutes, down 112-91.
That quartet engineered a rally and then Mazzulla inserted Tatum to join, sparking a 33-12 fourth-quarter ending run. The rally was a sign of greatness, but the Celtics can’t rely on those stretches to save them, even though on most nights it will.
“It’s a luxury, we’ve got a good group, we’ve got a good unit,” Brown said. “But we can’t take games for granted. We had an opportunity to win tonight and we didn’t pull through.”
Tatum and Brown know they didn’t play nearly at their level and the Celtics lost as a result. But they also saw how quickly they could flip the switch. Wednesday was a valuable lesson in a season that will present constant learning opportunities, even for a team this experienced.
“It was a tale of spurts,” Tatum said. “It showed when we played Celtics basketball, we don’t turn it over, we get back in transition and get stops and get out and run and play to our strengths, we’re a totally different team. In the other parts of the game, we didn’t do that and we didn’t look like ourselves.”
Gary Washburn is a Globe columnist. He can be reached at gary.washburn@globe.com. Follow him @GwashburnGlobe.