The Portuguese superstar headed home from close range in the second half, giving the Bianconeri a lead they wouldn't relinquish. Franck Kessie was sent off for Milan, while Gonzalo Higuain started on the bench and couldn't find the net against his parent club.
Both clubs were tied on seven Supercoppa titles entering the match.
For Juventus, it's their first win in three tries and revenge for the loss to Milan in 2016.
Allegri Has to Drop Dybala
Mario Mandzukic's injury has forced manager Massimiliano Allegri to alter his tactics to start 2019, and while the Bianconeri are two-for-two so far after the winter break, the former Milan boss should strongly consider dropping Paulo Dybala until the Croat returns.
The former Palmero man has never been a particularly strong wing player and didn't find much success in a false-nine role on Wednesday, either. With Ronaldo and Douglas Costa running the show on the wing, there was plenty of room for crosses, but the pint-sized Argentinian couldn't provide a good target.
Because of this, the threat from the wing was too easily neutralised, despite the strong play from Costa in particular. It took a spectacular ball over the top from Miralem Pjanic to break the deadlock:
The target of that ball was Ronaldo, who is better suited for a central role in the 4-3-3 formation Allegri has used without Mandzukic.
Dybala is still looking for his best form this season―he has just two goals in Serie A―and is a far better fit as the attacking midfielder in the 4-2-3-1 or 4-3-1-2 formations Allegri has sometimes used, combining Mandzukic and Ronaldo in the same starting XI.
Federico Bernardeschi built some nice chemistry with Ronaldo early this season before the injury bug struck, and he's now back to full health and rounding into form. The Italy international should slide into the team on the left wing, moving Ronaldo to the centre until Mandzukic returns.
Milan Must Find Higuain Replacement Before Agreeing to Chelsea Switch
Higuain seems to be closing in on a switch to Chelsea, where he will be reunited with former Napoli manager Maurizio Sarri, per the Guardian's Dominic Fifield and Fabrizio Romano.
The constant speculation received another boost on Wednesday when he didn't start against parent club Juventus, with Patrick Cutrone playing the majority of the contest as a lone striker. Broadcaster Matteo Bonetti wasn't buying Milan's excuse he was struggling with "fever:"
The young Cutrone played well and was unlucky not to score in the second half, smashing the crossbar. At the age of 21, he's one of Italy's best attacking talents, and the Rossoneri should lean on him heavily in the second half of the season, giving him every opportunity to continue his development.
But he has only bagged three goals in Serie A this season and still has a lot of growing to do. Milan need more, and they can't agree to any deal for Higuain before they add depth at the position.
There have already been some links, including to Genoa sensation Krzysztof Piatek:
Milan are still in the race for the UEFA Champions League tickets and can't afford to be left with limited options at the striker position by the time the window closes. With Alvaro Morata and Michy Batshuayi seemingly also on the move there may be possibilities there, but whatever the Rossoneri do, they have to make sure the deal is concluded before Higuain leaves.
If not, they run the risk of having to settle for a lesser option, or even worse, staying behind empty-handed.
Juventus will return to Serie A action against Chievo on Monday, while Milan will visit Genoa on the same day.