Paulo Dybala scored the only goal as Juventus cart home all three points from their visit to Old Trafford on Tuesday night.
The win over Manchester United ensured Juventus made it three wins from three in Group H.
Juventus, who have won all but one of their games in all competitions this season, were utterly dominant as Jose Mourinho’s men delivered another disappointing display on Tuesday.
Ronaldo was involved in Dybala’s winner, sending in a right-wing cross that ran into the forward’s path off a combination of Chris Smalling and Juan Cuadrado.
And although United improved after the interval – Paul Pogba hitting the post with a late curling shot – they were grateful to David de Gea for keeping the score down, the Spain goalkeeper making a world-class stop to keep out Ronaldo.
Dybala flashed an early header wide and former Juve star Pogba also wasted an aerial chance, nodding a free-kick from Ashley Young straight at Wojciech Szczesny.
But Juventus struck in the 17th minute when Ronaldo’s delivery from out wide deflected kindly for Argentina attacker Dybala to tuck away his fourth Champions League goal of the season.
De Gea denied Joao Cancelo before making a double save as Juventus continued to press, blocking a viciously swerving Ronaldo free-kick and then saving from Blaise Matuidi on the rebound.
The United goalkeeper was busy again after the break, making a wonderful save high to his left to keep out Ronaldo’s thunderous effort, while the hosts toiled at the other end.
Pogba almost snatched an undeserved point, his 75th-minute strike clipping the woodwork and bouncing clear off the diving Szczesny, but the Serie A champions held on to darken Mourinho’s mood.