Kevin De Bruyne was the most decisive player on the day, though teammate Claudio Bravo will dominate the headlines tomorrow.
City boss Pep Guardiola handed Bravo his full debut, while starting with Kelechi Iheanacho in attack. Jose Mourinho, meanwhile, pulled off a selection surprise, starting with Jesse Lingard and Henrikh Mkhitaryan.
The match, as expected, kicked off at a ferocious pace, with both teams testing eachother's defence.
However, it was City which took the lead inside the opening 15 minutes as Kevin de Bruyne took advantage of a slip by Daley Blind. De Bruyne nicked the ball away from the Dutchman before finishing superbly past David de Gea in the United goal.
From then on, it was one-way traffic as City dominated possession against a very flat looking United team. The visitors controlled possession and the pace of the game and it was no surprise when they went 2-0 ahead on 35 minutes.
De Bruyne was again at the heart of the move as his angled drive beat De Gea, but struck the far post. Kelechi was on hand to tap the ball past the flat-footed Spaniard.
City appeared set for a Saturday stroll, but United managed to pull a goal back just before halftime. Bravo fumbled a high Wayne Rooney free-kick, colliding with John Stones in the process. The ball fell for Zlatan Ibrahimovic, who managed to drive his volley beyond City defenders to have the score at 1-2.
The Swede should've sent the teams into halftime level as Bravo fluffed possession again. Ibrahimovic was presented with an easier chance than the goal, but could not get any power behind his shot, which was cleared away.
Rashford made an instant impact, testing City fullback Bacary Sagna several times. He set up Ibrahimovic for a half-volley, but the effort was skied.
The England youngster had the ball in the back of the net on 70 minutes, but it was disallowed for offside to Ibrahimovic.
Five minutes later, De Bruyne again threatened, striking De Gea's post.
A flashpoint came midway through the second-half, as Bravo and Rooney dived in for a 50-50 ball. The Chilean jumped in, but escaped punishment from ref Mark Clattenburg.
Rooney was later booked for a challenge on City's keeper.
The game finished with United laying siege on Bravo's goal. Rooney had an effort cleared off the line, as did Ibrahimovic and Paul Pogba.
But City managed to hold on to earn three points and a great personal triumph for the manager.