ATLANTA (AP) — Al Horford hit a huge 3-pointer against his former team and the Boston Celtics broke open a tight game in the closing minutes to finish off the Atlanta Hawks 128-120 on Thursday night for a 4-2 victory in the opening-round playoff series.

The second-seeded Celtics advance to face the third-seeded Philadelphia 76ers, who’ve been resting since completing their four-game sweep of Brooklyn last Saturday.

Game 1 is Monday night in Boston.

Boston ripped off an 11-0 run that included three straight 3-pointers, with Horford’s big shot sandwiched around 3s from Jayson Tatum and Jaylen Brown.

Tatum capped the spurt with a dunk, which gave the Celtics a 121-113 lead with 2:07 remaining.

Brown led the Celtics with 32 points, while Tatum had 30. Horford, who played in Atlanta from 2007-16, chipped in with 10 points and 12 rebounds.

After carrying the Hawks to an improbable victory in Game 5 at Boston, Atlanta’s Trae Young ran out of steam in the second half. He missed 12 of 13 shots over the final two quarters.

Young had 30 points and 10 assists, but he finished just 9 of 28 from the field.

Marcus Smart also came up big for Boston, scoring 22 points and brilliantly running the Boston offense down the stretch.

Dejounte Murray returned to the Hawks lineup after serving a one-game suspension for bumping an official at the end of Atlanta’s Game 4 loss.

Murray seemed a bit out of sync, missing all five of his shots in the first half. He was better in the second half but still managed just 14 points.

The Hawks needed a few more to keep their season going.

Young forced the series back to Atlanta with a long 3-pointer that stunned the Celtics 119=117 in Boston, capping the Hawks’ improbable comeback from a 13-point deficit in the fourth quarter.

Coming off his 38-point, 13-assist effort, Young kept it going with 18 points in the first quarter.

But the Celtics finally clamped down on the Hawks star, whose heroics had forced Janet Jackson to postpone her scheduled Thursday concert until Friday to make room for Game 6.

Now, State Farm Arena is wide open for the summer.

TIP-INS

Celtics: Boston finished 18 of 42 from 3-point range. Every Boston started made at least one from long range, as did three players off the bench. ... Malcom Brgodon had 17 points. ... Tatum led the Celtics with 14 rebounds.

Hawks: All five Atlanta starters scored in double figures. De’Andre Hunter had 20 points, John Collins added 16 and Clint Capela finished with 10. ... Onyeka Okongwu grabbed 11 rebounds.