The Celtics looked like they were going to suffer their first loss of the season in disastrous fashion. Instead, they staged a huge comeback to force overtime. But in the end it was all in vain. The Celtics lost an overtime thriller to the Pacers 135-132 in Indiana on Wednesday, suffering their first loss of the season. The Celtics fell to 4-1 on the season while the Pacers improved to 2-3.

Initially, the C’s kept pace with the Pacers early, helped by a buzzer-beater from Derrick White at the end of the first quarter. But Indiana just kept going in Boston and also gave the C’s their first double-digit deficit of the season. When the Pacers had a 24-point lead in the third quarter, they were in danger of knocking off the defending champions.

But midway through the fourth quarter, the energy changed. The Celtics went on a 33-12 run to force the Pacers into overtime and erase a 21-point deficit in less than nine minutes of play. Neemias Queta is partly credited with this run as he changed the balance with his play on the track. But the Pacers got the game-winning 3-pointer from Pascal Siakam in overtime and finally undid the C’s.

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Jayson Tatum led the C’s with 37 points and eight rebounds. Jaylen Brown had another 25 points while Derrick White had 23. Siakam was huge with 29 points and 11 rebounds – mostly from the stretch – for the short-handed Pacers, who were without big man Myles Turner. Bennedict Mathurin had another 30 points.

The Celtics continue their road trip and face the Hornets for their next game in Charlotte on Friday at 7 p.m. Here are four takeaways from Boston’s loss to Indiana:

Coming soon: It looked like the Celtics were quietly going to suffer their first loss of the season. Even as they cut the deficit to 14 points, the Pacers kept coming close early in the fourth quarter. Then some things changed for the Celtics. Queta’s energy was immediately noticeable as he seemed to be everywhere – this was reflected in his plus-18 rating in his 14 minutes. Queta also finished the game with two points and nine rebounds. The C’s also forced turnovers to put pressure on the Pacers. The fight that the Celtics missed early on, they finished late with the help of their substitutes. But they failed to finish the job as they lost for the first time this year.

Rotation folds: As the Celtics prepared their big comeback, it came without the backs of some key players like Payton Pritchard and Queta. What’s notable is that C’s coach Joe Mazzulla worked with the guys who lifted them up and breathed some life into them. Pritchard and Queta played through extra time. Pritchard in particular has earned significantly more trust because he had 16 points, four assists and four rebounds in 39 minutes of playing time. As a bonus, Jordan Walsh also got a few stints as he played eight minutes. This despite Sam Hauser returning after a three-game absence. So it’s a plus point for Walsh that he still had some playing time.

Defense test: While the Celtics defeated the Pacers in the East Finals last year, Indiana’s young team caused fits. It was more of the same earlier this season, as the Pacers gave the Celtics everything they could and more. The Pacers were relentless on offense and forced the Celtics back on their heels. Indiana finished with 62 points in the paint and 29 fast break points. These are staples of this Pacers style as they just kept the pressure on the Celtics. But the Celtics increased their intensity during the fourth quarter comeback, allowing just 12 points in the final 8:55 minutes to give them a chance.

Tough evening of filming: While Brown contributed elsewhere, it was a tough shooting night for the All-Star. Brown finished the game 1-for-11 on 3-pointers as he calmed down after a hot shooting start. Tatum was also 5 of 18 in 3 games, including 1 of 7 early in the game. But Tatum was able to improve his numbers by going 12 for 15 from the free throw line.