Making just his second start of the season in place of ailing Mickael Pietrus, Barnes scored a career-high 24 points, including 17 in the third quarter, to lead Golden State to a 91-78 victory on Saturday night.
Barnes also anchored the Warriors' 1-2-2 zone defense that stymied Utah's offense and helped hand the Jazz only their second loss of the season.
"I definitely don't think Utah was ready for it," Barnes said of the zone, installed just a day earlier by coach Don Nelson. "We definitely surprised them."
The Jazz shot just 32.5 percent from the floor and committed 23 turnovers while being held to their lowest point total of the season. It's just the second time this season Utah has been held below 100 points.
Utah, which had an eight-game winning streak snapped, still owns the best NBA's best record at 12-2 and has matched the best start in franchise history. Both losses have come on the road.
"We were just very casual and our team isn't good enough to be that way," Jazz coach Jerry Sloan said. "We won't be able to win any games if we try to play on a consistent basis that way."
The Warriors (8-6) never trailed and led by as much 20 points late in the fourth quarter.
One night after posting his previous career high with 21 points in a 140-129 loss to Denver on Friday, Barnes went 10-of-14 from the floor and grabbed seven rebounds before leaving the game after banging his knee against another player with 11:19 remaining.
"We have some people hurt and some people sick right now, so I'm just trying to get in there and hopefully establish myself in this rotation when we get back to full strength," Barnes said. "This was definitely a gut-check game for us after not showing up last night in Denver."
Utah rallied from second-half deficits to win each of its previous four games, including twice from 16 points down. But the Jazz had no such comeback in the tank against the Warriors, who won for just the third time in the last 24 meetings between the teams.
Matt Harpring scored 15 points for Utah.
Golden State played without leading scorer Baron Davis, who sat out his third straight game with a strained right rib muscle.
The Warriors led 43-42 at halftime and were still up by one when Barnes went to work in the third quarter. He scored on a three-point play with 9:20 left then had six more points during a 15-0 Golden State run that broke open the game.
Utah never could get going against the Warriors' 1-2-2 zone, which clogged the lane and prevented the Jazz from establishing any kind of offense underneath the basket.
"We had to try something new to cover one of the hottest teams in the league," Nelson said. "Who would have ever thought ... we'd be able to come in here and beat the best team in the West? Tonight the basketball gods were looking down on us."
The Jazz struggled through their worst opening quarter of the season, committing seven turnovers while shooting just 25 percent from the floor. The 14 points were a season low for Utah, which struggled with its half-court offense and failed to slow down a Golden State team minus its leading scorer and a second key starter.
Not that it seemed to matter to the Warriors.
Golden State went on a 14-2 run midway through the first quarter and led by as much as 30-16 on Barnes' 3-pointer with 11:08 remaining in the half.
The Jazz scored the last 10 points of the second quarter and pulled within 43-42 at halftime following Harpring's free throw that capped a 14-5 run.
- Davis has now missed 114 games over the past four seasons due to injuries.
- Sloan still needs four wins to become the fifth coach in NBA history with 1,000 career victories.
- The Warriors used their 10th different starting lineup in 14 games this season.
- Carlos Boozer was held to a season-low four points on 2-of-7 shooting for the Jazz after recording double-doubles in 11 of Utah's first 13 games.
- All five Golden State starters scored in double figures for the first time this season.