BOSTON — The Celtics completed a thrilling comeback 103-95 win over the Pacers on Monday at TD Garden. The bench came up huge for the C’s as they improved to 18-11 on the season. The Pacers dropped to 6-23.

The Pacers came into Monday’s game with the worst offensive rating and 3-point percentage in the NBA. That didn’t stop them from making 60% of their 3s in the first half to overwhelm the Celtics early. It was a 61-43 Indiana lead at halftime, and the C’s didn’t have many answers defensively.

Initially, it was more of the same for the Celtics to open the second half. But everything changed when C’s coach Joe Mazzulla benched his starters after an easy offensive rebound for the Pacers (more on this below). Suddenly, the game flipped as the reserves played with energy and life.

The Celtics went on to complete the comeback victory against the Pacers. It was another clutch game for the C’s, but they had all the momentum as Indiana struggled in the second half. The Celtics outscored them 60-34 in the second half.

Jaylen Brown led the Celtics with 31 points and nine rebounds, including 14 points in the fourth quarter. But it was the bench’s show Monday as part of a collective effort. Pascal Siakam had 25 points for the Pacers while Andrew Nembhard added 20 points and seven assists.

The Celtics rematch the Pacers at 7 p.m. Friday in Indiana for their next game. Here are four takeaways from Boston’s win over Indiana:

Pushing the right button: The Pacers made shots, but it’s not like the Celtics starters showed much life to open the second half. So, Mazzulla benched the starters with the C’s down 20 points to the Pacers. Brown, Derrick White, Payton Pritchard and Neemias Queta all sat. In came Anfernee Simons, Baylor Scheierman, Sam Hauser and Luka Garza. Hugo Gonzalez opened the second half with the starters, and he was the lone guy who stayed in the game after the switch. It was clear what message Mazzulla sent after the starters weren’t good enough. More importantly, the move worked. The bench group went on a 19-5 run to flip the game as the reserves outworked the Pacers on both ends. It was an imperfect group, but they breathed life into a game where the C’s were going through the motions.

Can’t stop this kid: Gonzalez is clearly playing the best basketball of his career, and Mazzulla leaned on him all night. He started the second half with the starters then didn’t sub out until there was less than a minute left in the game with the victory all but secured. The rookie finished with six points, 11 rebounds and two blocks. He was also a plus-23 in a career-high 37 minutes. It’s obvious he’s going to have a long NBA career as his relentless drive had him making plays everywhere on the court.

Difference in halves: The Pacers seemingly couldn’t miss from beyond the arc in the first half, making 12-of-20 of their 3-pointers. They did all that despite coming into Monday’s game with the worst 3-point percentage and offensive rating in the NBA. But they went ice-cold in the second half, making just 1-for-20 of their 3s. That allowed the Celtics to make their comeback effort Monday.

On the boards: Garza got another opportunity Monday after a solid showing against the Raptors last game. While the big man has his shortcomings defensively, there’s no denying his effort level. Garza’s physicality and rebounding were once again weapons for the Celtics. He finished with six points, nine rebounds (five offensive) and three assists in his 24 minutes, including playing 16 straight in the second half. Garza was also part of that bench group that flipped the game for the Celtics.