BOSTON — The Boston Celtics delivered a rude welcome to the Indiana Pacers at the start of the Eastern Conference finals.

The Celtics scored the game’s first 12 points in a raucous environment at TD Garden, and it was just the kind of message the Celtics needed to send.

The Pacers, however, shrugged it off. They are not strangers to unfriendly arenas having just beat the New York Knicks in a Game 7 Sunday at Madison Square Garden.

Indiana’s relentless offense got it back in the game, and the Pacers owned a 3-point lead with 46.8 seconds left in the fourth quarter. The Pacers then committed costly turnovers and failed to protect the lead.

It was a chaotic finish, punctuated by Indiana’s missed chances and Celtics star Jayson Tatum’s offense.

Boston’s Jaylen Brown made a tough corner 3-pointer with 6.1 seconds left to force overtime, and the Celtics outscored the Pacers in the five minutes of OT for a 133-128 victory in Game. 1.

Tatum followed a 3-point play with a 3-pointer from the top of the arc, giving Boston a 127-123 lead with 42.9 seconds to go, and it was enough cushion to escape with a victory.

Tatum scored a game-high 36 points and collected 12 rebounds and had three steals. He scored 10 points in OT and was one of three Celtics players with at least 26 points, seven rebounds and three steals. Brown had 26 pints, six rebounds, five assists and three steals, and Jrue Holiday produced 28 points, eight assists, seven rebounds and three steals.

Game 2 is Thursday in Boston (8 p.m. ET, ESPN).

Offense on display

The Celtics had the No. 1 offense and the Pacers the No. 2 offense during the regular season. The scoring prowess was apparent. Both teams hovered at the 50% mark from the field with Boston 47.5% and Indiana at 53.5%, and seven Pacers scored in double-figured led by Tyrese Haliburton’s 25 points and 10 assists. Pascal Siakam had 24 points, 12 rebounds and seven assists and Myles Turner added 23 points and 10 rebounds for the Pacers.

While Boston had the league’s No. 2 defense, Indiana’s plan is to apply as much pressure as possible with their pace. But among the difference-makers in this game: Indiana's turnovers. The Pacers committed 22 turnovers, leading to 32 Celtics points.

Horford continues to fill in for Kristaps Porzingis

Veteran big man Al Horford, who is in the starting lineup for the injured Kristaps Porzingis, had 15 points and six rebounds. He doesn’t place what Porzingis does but his experience helps minimize Porzingis’ absence. Porzingis hasn’t played since Game 4 of the first round because of strained right calf. He is targeting a possible Game 4 return, ESPN reported on Tuesday.

Free throw discrepancy

The Celtics shot 30 free throws, making 24, and the Pacers were just 9-for-10 from the foul line with seven of those attempts coming overtime. That’s in a part a byproduct of how both teams play. Pacers coach Rick Carlisle complained about the officiating during the Knicks series, and the NBA fined him $35,000 for “public criticism of the officiating and questioning the integrity of the league and its officials,” the league said in a news release.