Donovan Mitchell added 11 points, and Rudy Gobert had nine points, seven rebounds and three blocks. The Jazz won their third straight at Boston, capitalizing on the short-handed Celtics' shooting woes.
"It's a big win. Coming into Boston, it's very tough to play here," Conley said. "They have a great team, well coached. For us all to come out and just play with the passion that we played with and just compete the way we did. For us to come in and just be aggressive, be assertive at all times was a lot of fun."
Boston couldn't overcome Utah's torrid shooting that the Jazz rode to a 16-point lead in the second quarter.
"It's on us. I don't know what's going on out there. It's like we let other teams' pressure take us out of the game," Smart said. "When that happens, this is the outcome. We've got to fix that. We've got to be the aggressor."
The Jazz led 62-49 at halftime after shooting 60.5 percent (23 for 38) in the first two quarters. Utah hit 13 of 21 3-pointers in the half, going 8 for 11 from long distance in the second quarter.
The Celtics opened the third quarter on an 11-3 run that got Boston right back in it, but only briefly. Tatum's free throw after a technical foul on Mitchell pulled Boston to 66-61, but Royce O'Neale answered with a 3-pointer -- the first of the second half for the Jazz -- and Utah quickly pushed the lead back up to double-figures, taking a 79-66 lead into the final period.
A three-point play by Brad Wanamaker pulled Boston within 87-78 with 6:54 remaining, but Boston never threatened and a 3-pointer by Smart just before the final buzzer made the outcome seem closer than it was.
The Celtics led by as much as 11 in the first quarter, making 12 of their first 23 shots, but still couldn't keep up as Utah surged late in the period and continued with Utah.
"I think really Boston came out hot and it would've been easy to look around, say 'what's going on?' -- and we just dug in," Jazz coach Quin Snyder said. "We just kept doing the same things. We did them better."
Utah entered the game leading the NBA in 3-point shooting percentage at 38.5% despite an off night in a win Wednesday at New York. The Jazz were back on target from outside Friday, making 17 of 45 3-pointers. Conley, who has struggled some in his first season with Utah, led the way, hitting four 3-pointers in the first half and adding two more after halftime.
"I feel good, man. I feel really good. I'm in a great place. My teammates have been behind me this whole time," Conley said. "It's been a frustrating road for all of us because they know how good I am and I know how good I am.
Jazz: Closed the first quarter on a 14-2 run and led 30-29 entering the second period. ... Utah's three straight wins at Boston are the most for the Jazz since winning seven in a row from 1992-99. ... Mitchell was called for a technical foul with 6:21 left in the third after complaining about a call.
Celtics: Brown (right hamstring strain) and Hayward (right knee contusion) were both out of the lineup for the second straight game with injuries. ... Smart, fined $35,000 by the NBA Thursday for confronting officials after Tuesday night's overtime loss to Brooklyn, turned 26 on Friday. ... Smart was called for a technical foul with 9:01 left in the fourth.
Jazz: Wrap up a four-game trip at Detroit on Friday night.
Celtics: Host Oklahoma City on Sunday night.
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