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."
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.
"At Juventus winning is not important. It's the only thing that counts."
"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."
