He got it on a night that included Boston's remembrance of the player Tatum said first made him want to pick up a basketball.
Marcus Smart added 21 points, scoring 17 in the second half on a night when Boston became the latest team to offer a tribute to Bryant following his death in a helicopter crash.
Tatum, who was named to his first All-Star team before the game, returned to the lineup after missing three games with a right groin strain. He finished with 20 points in 24 minutes.
''It's been a tough week,'' Tatum said. ''I feel like I ain't played in a month. It was fun to just be out there in front of our fans and just be out there with the guys. I missed it.''
Tatum said he found out he'd earned the All-Star nod during pregame warm-ups.
''I wanted to cry,'' he said. ''I didn't cry. I might cry later, though. ... I've been watching the All-Star Game ever since I've been watching basketball. I would always get Kobe's All-Star jersey. I had aspirations of one day being in the All-Star Game. At 21 years old to make it a reality ... It's a special feeling.''
D'Angelo Russell led the Warriors, who lost their fifth straight, with 22 points. Alec Burks scored 18.
The Celtics trailed in the opening minutes of the first quarter, but closed out the final 5:48 of the period on an 18-7 run to edge in front. Boston led by as many as 19 in the fourth quarter.
It was the Celtics' first home game since Bryant, his 13-year-old daughter Gianna and seven others were killed in Sunday's crash in Calabasas, California.
In the pregame, rivalry took a backseat to remembrance of the Lakers star.
It normally would be unheard of for any player associated with Boston's longtime nemesis to get a standing ovation in the Celtics' arena.
It happened Thursday in honor of one of the NBA's greatest players.
Bryant's No. 24 was illuminated in lights on the court as Celtics fans joined the organization for 24 seconds of silence. Then, following a video tribute that included cameos from current and former Celtics, the arena erupted in cheers.
''It was cool to see,'' Tatum said. ''He definitely deserves that.''
Said Warriors forward Draymond Green: ''Just to see so many Kobe jerseys on these Boston fans was special.''
Warriors: Outscored the Celtics 27-10 in fast break points. ... Were outrebounded 37-27.
Celtics: Finished with 23 turnovers. ... Made seven 3-pointers in the third quarter after hitting four in the first half. ... C Enes Kanter missed his fourth straight game with a right hip contusion.
YOUTH IS SERVED
Tatum joined Walker as the Celtics' All-Star selections. Walker was voted in as a starter last week. According to the Elias Sports Bureau, at 21 years and 333 days Tatum is the second-youngest Celtics player selected to an All-Star game behind Antoine Walker, who was 153 days younger. Tatum wore sneakers from Bryant's Nike collection during pregame warmups.
Warriors: Visit Cleveland on Saturday.
Celtics: Host 76ers on Saturday.
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