Match ends, Manchester United 0, Juventus 1.
Cristiano Ronaldo marked his return to Old Trafford with a win as his Juventus side saw off Manchester United to move five points clear at the top of Champions League Group H.
The former United star helped to set up Juve's winner in the 17th minute, with his cross reaching Paulo Dybala who finished from close range.
The Italian champions had several chances to extend their lead during a first half where they were completely dominant, managing 10 shots to United's one and enjoying 70% of possession.
United improved after the break but only had one serious effort at goal, when Paul Pogba let fly from the edge of the area but saw his shot rebound off the post.
It was a frustrating night for United boss Jose Mourinho, who was taunted by the away fans as he saw his side suffer only their second home European defeat since March 2013, when Ronaldo scored Real Madrid's winner.
The two sides will meet again at the Allianz Stadium on 7 November, when a win will send Juve into the last 16.
United remain in second place, with their hopes of making the knockout stages boosted by Valencia's draw with Young Boys earlier on Tuesday.
Ronaldo had returned to Old Trafford with a rape allegation - that he strenuously denies - hanging over him but said before the game that he is "a happy man".
All eyes were on him again from the moment he led his team-mates out of the tunnel for the warm-up, and he received an enthusiastic welcome from the home fans as well as the travelling Juve supporters.
As was so often the case during his six years as a United player between 2003 and 2009, Ronaldo was to play a starring role when the game got under way.
The 33-year-old's performance, particularly in the first half when Juventus were completely dominant, was a reminder of his former glories here and a time when United were a team renowned for their attacking flair.
He started the game on the left but Juve's fluid front three meant he often popped up on the right, as he did to set up Juve's goal, or in the centre.
The Portuguese forward could not cap his display with a goal - David de Gea's fine save to tip over his curling shot shortly after the break was his best effort - but this was still an impressive demonstration of his enduring quality.
Ronaldo remained the centre of attention after the game too. A succession of pitch invaders attempted to reach him during the match and after the final whistle, when he took a selfie with one of them.
That meant he was the last player to leave the pitch, and he was cheered off by all sides of Old Trafford, while clapping and touching his chest to show what their applause meant to him.
United have mounted second-half comebacks in their last two matches, a victory over Newcastle and their draw with Chelsea last weekend, but they did not come close to a repeat here.
Those performances had hinted at what United are capable of when they hit form but this game turned into a sobering reminder of their standing compared to Europe's elite, particularly in attack.
Anthony Martial finally forced Wojciech Szczesny into one save of note with seconds of the 90 minutes remaining, with the Juve keeper's only other stop coming before the break when he collected a looping header from Pogba.
Like Ronaldo, the France midfielder was also facing his former club - it was during his four years with Juve from 2012-16 that Pogba forged his reputation as a world-class marauding midfielder.
But he was unable to inspire his side in the final third, while Romelu Lukaku's goal drought continued, and must now be becoming a major concern.
The Belgium striker only managed one shot at goal - which was blocked - and he has now failed to score in any of his past eight club appearances.
Manchester United manager Jose Mourinho: "In the other side there was huge quality. Sometimes people look for Ronaldo or Dybala but in a top team you have to look to Chiellini and Bonucci. I think Juventus are the type of team that when they are in front its very difficult.
"I think our attacking players, things were not coming. But everyone tried, everyone was strong mentally to try until the end. Juventus felt it and they ended the game with an extra central defender.
"But Juventus is a different level of quality, I have to be honest. A level of quality, stability, experience, know how. It was a really difficult match for us. I thought we could take something but it was not possible."
United's next test is a home game against Everton on Sunday (kick off at 16:00 GMT). Juventus, who dropped their first domestic points of the season last weekend in a draw with Genoa, travel to play Empoli on Saturday (17:00).
Match ends, Manchester United 0, Juventus 1.
Second Half ends, Manchester United 0, Juventus 1.
Attempt blocked. Cristiano Ronaldo (Juventus) right footed shot from outside the box is blocked. Assisted by Blaise Matuidi.
Attempt saved. Anthony Martial (Manchester United) right footed shot from outside the box is saved in the bottom right corner. Assisted by Nemanja Matic.
Attempt missed. Leonardo Bonucci (Juventus) right footed shot from outside the box is too high. Assisted by Miralem Pjanic.
Corner, Juventus. Conceded by Victor Lindelöf.
Foul by Blaise Matuidi (Juventus).
Chris Smalling (Manchester United) wins a free kick in the defensive half.
Substitution, Juventus. Douglas Costa replaces João Cancelo.
Offside, Manchester United. Marcus Rashford tries a through ball, but Juan Mata is caught offside.
Hand ball by Cristiano Ronaldo (Juventus).
Corner, Manchester United. Conceded by Leonardo Bonucci.
Attempt blocked. Romelu Lukaku (Manchester United) left footed shot from the left side of the box is blocked. Assisted by Anthony Martial.
Offside, Juventus. Miralem Pjanic tries a through ball, but Federico Bernardeschi is caught offside.
Giorgio Chiellini (Juventus) is shown the yellow card.
Miralem Pjanic (Juventus) wins a free kick in the defensive half.
Foul by Ashley Young (Manchester United).
Substitution, Juventus. Andrea Barzagli replaces Juan Cuadrado.
Foul by Rodrigo Bentancur (Juventus).
Marcus Rashford (Manchester United) wins a free kick on the left wing.
Hand ball by Giorgio Chiellini (Juventus).
Leonardo Bonucci (Juventus) wins a free kick in the defensive half.
Foul by Marcus Rashford (Manchester United).
Substitution, Juventus. Federico Bernardeschi replaces Paulo Dybala.
Ashley Young (Manchester United) is shown the yellow card.
Alex Sandro (Juventus) wins a free kick in the defensive half.
Foul by Ashley Young (Manchester United).
Paul Pogba (Manchester United) hits the left post with a left footed shot from outside the box.
Cristiano Ronaldo (Juventus) wins a free kick in the defensive half.
Foul by Chris Smalling (Manchester United).
Rodrigo Bentancur (Juventus) wins a free kick in the defensive half.
Foul by Anthony Martial (Manchester United).
Offside, Juventus. Cristiano Ronaldo tries a through ball, but Paulo Dybala is caught offside.
Paulo Dybala (Juventus) wins a free kick in the defensive half.
Foul by Ashley Young (Manchester United).
Blaise Matuidi (Juventus) is shown the yellow card for a bad foul.
Foul by Blaise Matuidi (Juventus).
Ashley Young (Manchester United) wins a free kick on the right wing.
Offside, Manchester United. Juan Mata tries a through ball, but Nemanja Matic is caught offside.
Foul by Rodrigo Bentancur (Juventus).