Anthony Martial and Scott McTominay secured Manchester United a stunning third derby victory of the season as Ederson endured a dismal afternoon in the Manchester City goal.
There was skill, tension and no little controversy as these bitter rivals met in the top flight for the 150th time, with Pep Guardiola's men looking to gain bragging rights at a ground that has been so good to them recently.
But the City boss would lose his first Premier League match at Old Trafford as Ederson floundered, having failed to deal with Martial's superb volley before gifting McTominay the chance to add stoppage-time gloss as the Manchester derby ended 2-0.
United's first home league win in the Manchester derby since April 2015 was a welcome shot in the arm as they bid to qualify for the Champions League, although the result may hasten bitter rivals Liverpool's title triumph.
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But the Old Trafford faithful will not care after the hosts held firm during a strong City start and went ahead through a stunning set-piece routine – from a free-kick City could not believe was given, following a challenge on Bruno Fernandes by Ilkay Gundogan – as Fernandes' delicate clipped ball over the back line was volleyed through Ederson's grasp by Martial.
United were soon aggrieved when Fred was shown a yellow card for diving in the box despite Nicolas Otamendi making contact.
The controversial lack of VAR intervention on that decision would have been even harder for the home team to swallow had Sergio Aguero's goal stood at the start of the second half given United had all but downed tools with the flag raised.
Ederson was counting his blessings moments later after denying Martial with a tackle, having uncharacteristically miscontrolled at the start of a second half that City dominated.
But the hosts held firm as the rain fell, with Ederson's poor throw returned with interest by McTominay at the death as United added to this season's league and Carabao Cup wins at the Etihad Stadium.
Elated Ole Gunnar Solskjaer punched the air at the end of an encounter that United began unconvincingly.
David De Gea got down to stop Raheem Sterling's curling effort after Luke Shaw overplayed, before Nemanja Matic saved Harry Maguire's blushes having allowed Aguero through.
United saw out the early storm and began to build momentum, with Daniel James testing Ederson before Fernandes fumed at Martial for shooting rather than laying it back.
But the pair buried the hatchet in style in the 30th minute.
City raged at the decision to award a foul against Gundogan, with Fernandes going down and then catching the visitors napping from the resulting free-kick. Martial met the superb, pre-planned ball over with a hard, low volley that Ederson let through at his near post.
Fernandes miscued a header as United looked for a second before Fred was controversially booked for diving. Replays showed Otamendi looked to have caught the Brazil international, but strangely there was no VAR intervention.
However, VAR Andre Marriner was alert minutes after the restart.
De Gea watched Aguero find the net with the offside flag long since raised, but the call was checked and the initial decision given the green light by the slightest of margins.
United were relieved, just as Ederson would be soon after.
Normally so superb in possession, his poor control saw the ball trundle towards his goal-line and required him to deny Martial with a last-ditch recovery challenge.
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It was a wild start to a second half that City mostly spent on top. Phil Foden's fizzing 25-yard effort forced De Gea to tip over as the visitors pushed for a leveller and Otamendi headed over from a corner as United continued on the back foot.
City's attacking intent was giving United the chance to break at speed and Solskjaer was as furious as Fernandes that James shot rather than passing.
Sterling wasting a fine chance from Riyad Mahrez's cross and De Gea denied Gabriel Jesus as tension mounted.
The pressure was released in some style deep in stoppage time as Ederson threw directly to home-grown midfielder McTominay, whose first-time strike from distance found the net in front of a bouncing Stretford End.