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.

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Jayson Tatum drives

Jayson Tatum #0 of the Boston Celtics dribbles the ball during the game against the Atlanta Hawks during Round 1 Game 6 of the 2023 NBA Playoffs on January 1, 2023 at State Farm Arena in Atlanta, Georgia.  (Adam Hagy/NBAE via Getty Images)

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.

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Trae Young makes crying eyes

Trae Young #11 of the Atlanta Hawks reacts after a basket against the Boston Celtics during the second quarter of Game Six of the Eastern Conference First Round Playoffs at State Farm Arena on April 27, 2023 in Atlanta, Georgia.  NOTE TO USER: User expressly acknowledges and agrees that, by downloading and or using this photograph, User is consenting to the terms and conditions of the Getty Images License Agreement. (Kevin C. Cox/Getty Images)

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.

Jaylen Brown drives

Jaylen Brown #7 of the Boston Celtics drives against Saddiq Bey #41 of the Atlanta Hawks during the second quarter of Game Six of the Eastern Conference First Round Playoffs at State Farm Arena on April 27, 2023 in Atlanta, Georgia.  (Kevin C. Cox/Getty Images)

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