BOSTON -- Rookie Jayson Tatum scored 21 points and hit a pair of free throws in the closing second, and the Boston Celtics rallied from a 22-point deficit to beat the Philadelphia 76ers 108-103 on Thursday night and take a 2-0 lead in the Eastern Conference semifinals.

Terry Rozier added 20 points, nine assists and seven rebounds. Marcus Smart finished with 19 points and five rebounds as the Celtics improved to 6-0 at TD Garden this postseason. They have never blown a 2-0 lead.

Game 3 is Saturday in Philadelphia.

J.J. Redick had 23 points for the 76ers, making five 3-pointers. Robert Covington added 22 points and nine rebounds. Joel Embiid finished with 20 points, 14 rebounds and five assists, but rookie star Ben Simmons missed all four shots and had just one point.

Philadelphia recovered after squandering its big lead to nudge back in front 93-88 midway through the fourth quarter.

But an 11-4 run put Boston back in the lead 99-95 with less than four minutes to play.

It was 101-97 when a missed Philadelphia jumper led to a 2-on-1 fast break and alley-oop dunk from Rozier to Tatum with 2:23 left.

A layup by Dario Saric cut it to 104-101. But Al Horford was able to drive past Embiid for a layup with 8.3 seconds left.

Saric scored out of a timeout to make it 106-103. The Sixers quickly fouled Tatum, who calmly hit a pair of free throws.

Following an anemic offensive effort in Game 1, the Sixers looked rejuvenated early in Game 2, using a 14-2 run to begin the second quarter on their way to building a 48-26 lead.

It didn't last.

The Celtics responded by ending the half on a 25-8 run. It included three straight 3-pointers and a tip-dunk by Jaylen Brown, who returned to action after sitting out the series opener with a strained right hamstring. He came off the bench and played 25 minutes, scoring 13 points and grabbing four rebounds.

The Sixers' lead was completely erased midway through the third quarter, when Aron Baynes got a 3-pointer to bounce in and put Boston in front for the first time.

The lead grew to 76-68 on a baseline dunk by Tatum that capped a 50-20 Celtics run.

Brown entered the game for the first time at the 7:14 mark of first quarter. It took less than a minute to make an impact. He missed his first shot attempt before chasing down a loose ball and sprinting ahead for a one-handed dunk .

Prior to Thursday, Brown had started every game he'd appeared in this season. It was his first time off the bench since Game 5 of last season's Eastern Conference Finals.

TIP-INS

76ers: Outrebounded the Celtics 49-41. ... Went 13 of 33 from the 3-point line.

Celtics: Went 15 of 36 from the 3-point line. ... Held a 19-13 edge in fast-break points and 30-23 in bench scoring.

SLOW START

Despite Brown's early highlight, the Celtics were sluggish early.

They started off the game 0 for 5 and didn't score until Smart's 3-pointer at the 8:37 mark of the first quarter.

Horford (1 for 3), Rozier (0 for 4), Brown (1 for 4) and Marcus Morris (0 for 3) were a combined 2 for 14 in the period, allowing Philadelphia to build a 31-22.

FACE OFF

Brown caught an inadvertent slap across the face from Covington on a layup attempt late in the second quarter. Brown stayed down briefly as the Sixers proceeded to fast break.

Following a Philly miss Brown, who was still standing under Boston's basket, caught a long outlet pass and was fouled hard by Covington. But Brown wanted no part of Covington helping him to his feet, and violently brushed back his hand.

CELEB SIGHTINGS

Philadelphia-born rapper Meek Mill sat courtside for Game 2. Mill was released from jail last week after spending nearly five months behind bars on a probation violation. Rapper Gucci Mane sat across from the 76ers bench wearing a Brown jersey. The two met last year when Brown attended one of his concerts.

Another Philly native, actor Kevin Hart, sat a few seats down from Gucci. Hart at times antagonized the TD Garden fans, drawing boos.