NBA: Playoffs-Indiana Pacers at Boston Celtics

Celtics guard Kyrie Irving drives to the basket while Pacers guard Wesley Matthews defends during the second half of the Game 1 of the NBA playoff series Sunday, April 14, 2019.

BOSTON — They came out tight, turned it over 10 times in the first half, got everyone to wondering about their worst habits, and that seemed to be enough.

The Celtics, on the power of an explosive second half, took Game 1 of their first-round playoff series against Indiana with a 84-74 win on Sunday.

Game 2 is Wednesday night at TD Garden.

The Celts’ 22-3 run over the first 8:04 of the third quarter coincided with an arctic stretch from the Pacers, who missed 12 of their first 13 shots and finished the third 2-for-19 from the floor with five turnovers.

For a Celtics team that had shot 13-for-40 in the first half, and thanks to a revived Marcus Morris (15 first-half points), trailed by seven points (45-38) after the first 24 minutes. The halftime break appeared to make all of the difference.

Kyrie Irving overcame a seven-point, 3-for-10 start to finish with 20 points on 6-for-17 shooting, and Morris matched him with 20 points and seven rebounds.

Terry Rozier’s 3-pointer runner with a second left in the third quarter was good for a 64-53 lead after a third quarter that couldn’t have been more lopsided for both sides. The Celtics carved out their lead thanks to a quarter-opening 22-3 run, with the Pacers missing 12 of their first 13 shots.

The Celtics, thanks to a pair of Tyreke Evans misses at the line, also ran off the first four points of the fourth quarter, including a Hayward transition drive off a Horford feed that triggered an Indiana timeout.

Cory Joseph scored for Indiana with 9:03 left, and the run continued with Tatum and Irving burying consecutive bombs, extending the run to 10-2 and the lead to 74-55.

Three-pointers from Al Horford and Tatum down the stretch helped keep the Pacers at arm’s length the rest of the way.

As evidenced by Irving’s seven-point, 3-for-10 first half, and the 10 Celtics turnovers Indiana converted into 11 points, the Celtics could probably feel fortunate for trailing by only a 45-38 halftime score.

Save for Morris’ 15-point performance off the bench, the Celtics were a tentative lot when put under pressure by the Pacers, one of the league’s best defensive teams.

And then something popped at both ends. As the Pacers were missing their first 11 shots of the third quarter (and 12 of their first 13), finally breaking the ice when Horford goaltended a Cory Joseph drive, the Celtics opened with a crushing 22-3 run.

Brown started it with his first basket of the game, and Morris capped the burst with his third 3-pointer of the afternoon for a 60-48 lead.

The Pacers regrouped, slightly, with a 7-0 run, before Rozier added an explosive kick, hitting the second of two free throws with 30.6 seconds left in the third, and then following up a Sabonis miss with a running 3-pointer at the buzzer for a 64-53 Celtics edge.

The Celtics, tied 20-20 at the end of the first quarter despite six turnovers and 39 percent shooting, had Morris to thank for being in such good shape.

When the starting unit misfired, over-passing its way into an eight-point deficit, Morris and Hayward were quickly sent in, with the former hitting a corner three on his way to 12 points over the last 5:29 of the quarter.

But they continued to throw the ball away under pressure from the Pacers, giving up a 9-0 run early in the second quarter, and then a 7-0 mid-quarter burst capped when Collison converted a Tatum throwaway.

Threes from Tatum and Irving over the next minute helped the Celtics regroup, eventually cutting the Indiana lead to 45-38 on Hayward’s transition layup.