Juve, 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 Juve 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 Juve 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.
What it means: Problems mount for Mourinho
United have won once in their last seven matches and Mourinho - whose side arrived late for the second home Champions League game in a row - had to watch his side receive a footballing lesson at Old Trafford. Juve, meanwhile, look like serious contenders for the title after a supreme showing maintained their 100 per cent record in the group. There is work to do for United to qualify, but they should still edge out Valencia and Young Boys.
Chiellini in cruise control
Mourinho has regularly bemoaned his defensive options and he must wish he had a player of Giorgio Chiellini's class and poise. The Juve skipper did not put a foot wrong, even setting up an attack by selling Marcus Rashford an outrageous dummy. Chiellini's partner Leonardo Bonucci - who revealed on the eve of the game he had turned down a move to United - also excelled, producing one terrific tackle to deny Anthony Martial.
Pogba lacks influence
France midfielder Pogba was looking forward to an emotional reunion with Juve but he struggled to exert his influence on the contest. He was outshone by a relative rookie as Rodrigo Bentancur helped the away side dominate the midfield battle for Juve, although Pogba did come close to equalising for United.
Key Opta Facts:
- Manchester United suffered their fourth home defeat in their last 13 games at Old Trafford in all competitions – as many as in their previous 81 home matches.
- Juventus registered their first win at Old Trafford in the Champions League since November 1996, when they won 1-0 under manager Marcello Lippi.
- Manchester United failed to score in consecutive home Champions League matches for the first time since November 2005.
- Only Lionel Messi and Edin Dzeko (5) have scored more Champions League goals this season than Juventus striker Paulo Dybala (4).
- Manchester United attempted six shots, their fewest in a home Champions League game since April 2014 against Bayern Munich (also six).
- Juventus are unbeaten in nine European matches against English opposition (W5 D4), last losing in March 2010 against Fulham in the Europa League.
78 - Rodrigo Bentancur completed the most passes (78) in the game between Manchester United & Juventus, with 91% passing accuracy. Director. pic.twitter.com/P2tuN6E6aZ— OptaJavier (@OptaJavier) October 23, 2018