Juve manager Luciano Spalletti watched from the stands after receiving a one-match touchline ban following his red card against Cagliari last Sunday, with assistant boss Marco Domenichini patrolling the technical area instead.
This may have affected the hosts, who at times struggled to cope with Lazio’s intensity, although in-form striker Randal Kolo Muani saw a 24th-minute goal disallowed after volleying home from an offside position.
Both Kolo Muani and Isaksen scored in their sides’ previous league games, and the latter had Lazio’s first clear chance when he floated a header wide on the half-hour mark.
The Biancocelesti took the lead in the same way eight minutes before half-time, when Mattia Zaccagni clipped in an inviting cross, and Provstgaard nodded in his first goal for the club from six yards out.
Nuno Tavares almost doubled the lead six minutes later, as his shot from the edge of the box deflected off Gleison Bremer and looped onto the top of the crossbar.
The first-half clean sheet maintained Lazio's impressive record, leaving them as one of just two Serie A teams pre-round to concede before the break.
Juve lacked attacking quality in the opening 45 minutes, and Nick Woltemade replaced Kerim Alajbegovic at half-time in a bid to change that.
However, the German striker scuffed a presentable chance wide 10 minutes after the restart, and that proved costly when Isaksen cut inside and whipped a shot into the net midway through the half, the Dane’s second goal at Allianz Stadium in as many seasons.
Kolo Muani headed a chance over the bar, but it was Lazio who scored late on as substitute Fisayo Dele-Bashiru raced clear before firing his first goal of the campaign low past Guglielmo Vicario.
The victory extends the Biancocelesti’s unbeaten start to the season and sees them return to second place in the table, level on points with leaders Inter Milan. While marking a milestone for Gattuso, it is also the first time the Biancocelesti have won six of their opening seven league games, including four successive away wins.
Meanwhile, Lazio’s first league win at Juventus since 2017 extends the Bianconeri’s poor run to one victory in five matches (D2, L2) and ends their unbeaten start at home, leaving Spalletti’s side eighth in the table.
Flashscore Man of the Match: Oliver Provstgaard (Lazio)