The combative midfielder netted his first goal in three league seasons and only his eighth goal in 12 Serie A campaigns with Milan when his shot surprised Juve goalkeeper Gianluigi Buffon midway through the second half.
Gattuso starts a five-match European ban when Milan visit Tottenham Hotspur in the Champions League last 16 on Wednesday following his headbutt on Spurs assistant boss Joe Jordan in the first leg which the Rossoneri lost 1-0.
"There's still a long way to go but my goal is an important one," the 33-year-old told Sky television as Milan eye their first league title since 2004.
"Sometimes the coach has to interrupt training because there is too much competitiveness. Every time there has been this sort of atmosphere at the Milanello training ground we have won the scudetto."
Milan deserved their victory with Zlatan Ibrahimovic wasting a good early chance while Juve were rarely a threat.
Juve's third defeat in a row leaves coach Luigi Del Neri under huge pressure after a season which was meant to spark a revival for Italy's best supported and most successful domestic club after last term's seventh-placed finish.
Some media reports said before the game that the coach would be sacked if they lost against their arch-rivals and remained in seventh. Club officials had just given vague backing.
Angry home fans unveiled a banner at halftime in Turin including a phrase often uttered by former striking great Giampierio Boniperti.
"At Juventus winning is not important. It's the only thing that counts."
Del Neri, who left out Alessandro Del Piero and Italy centre back Leonardo Bonucci, hinted his expensive group of players are just not good enough compared to Juve sides of the past with the club still recovering from a 2006 match-fixing demotion.
"At the moment our quality is a lot more inferior to Milan," he said. "We must try to play better. If as individuals we are lacking then you need to compensate as a group."
