BOSTON — Jaylen Brown scored 31 points to lead the Celtics back from a 20-point deficit to beat the Pacers 103-95 on Monday night at TD Garden as Boston outscored the Pacers 60-34 in the second half.

The Pacers lost their fifth straight game to fall to 6-23. The Celtics have won three straight and improved to 18-11.

Derrick White added 19 points for the Celtics. Guards Peyton Pritchard and Anfernee Simons scored 11 each. Pascal Siakam led the Pacers with 25 points. Guard Andrew Nembhard added 20 and seven assists. Guard Bennedict Mathurin had 16 points and nine rebounds. Guard Ethan Thompson added 13 points.

Here are three observations.

Pacers sizzle from 3, then freeze

The Pacers had their worst 3-point shooting night in a terrible shooting season on Saturday night, hitting just 8 of 42 attempts (19.0%) to sink further into last place in the NBA in 3-point shooting percentage at .323. On Monday, the Pacers seemed to have that script totally turned around … until they didn’t.

The first quarter was one of the Pacers’ best shooting periods of the season as they knocked down 8 of 12 3s to match Saturday night’s total. At halftime, they were 12 of 20 from 3 and held a 61-43 halftime advantage despite scoring just 12 points in the paint up until that point. They were 21 of 41 from the floor and 15 of those buckets were either 3s or mid-range jumpers.

But when the Pacers’ shooting magic left them it disappeared all at once. They missed their first eight 3-pointers of the second half and after Andrew Nembhard finally made one, they missed their next 12 after that. They weren’t any better at getting to the rim and they allowed what was a lead of as great as 20 points to disappear entirely. The Pacers finished with just 34 second-half points on 12 of 44 shooting including 1 of 20 from 3-point range. In the fourth quarter, they scored just 13 points on 4 of 18 shooting, missing all eight of their 3-pointers. The Celtics not only won, they at one point built a 10-point lead and outscored the Pacers 60-34 after the break.

Jaylen Brown goes wild in the second half

Jaylen Brown has had to step into the superstar role for the Celtics this year with Jayson Tatum out for most if not all of the year with an Achilles tendon tear. The Pacers kept him from putting up All-Star numbers in the first half, but once Brown got rolling, he couldn’t be stopped.

Brown had just 11 points on 4 of 12 shooting in the first half with Nembhard taking on the primary assignment and keeping him away from the rim. But he kept driving the ball and he got better from the mid-range and from distance and in the second half the Pacers had no answer for him. He was 7 of 13 from the floor for 20 points in the final 24 minutes to finish with 31 for the game.

Pascal Siakam makes one second-half field goal

While the Celtics All-Star stepped up with a dominant second half after a spotty first two quarters, the Pacers All-Star nearly disappeared after a brilliant first half.

Pascal Siakam spearheaded the Pacers’ first-half barrage and seemed set for one of his best games of a season when he’s so often had to carry this team. He had 23 points at the break on 8 of 11 shooting and was 4 of 5 from beyond the arc, his offensive game working at the rim, in the mid-range and from distance.

But when the bottom fell out for the Pacers, Siakam wasn’t there to stop it. He made just 1 of 7 second-half field goals to finish with two points after halftime.

Dustin Dopirak covers the Pacers all season. Get more coverage on IndyStarTV and with the Pacers Insider newsletter.