This was a derby that meant more to Manchester United than Manchester City – and it showed on the pitch.
For half of Sunday's game at Old Trafford, Pep Guardiola's men simply failed to match the home side's intensity, with their unusual sluggishness and resulting sloppiness summed up by Ederson.
The Brazilian goalkeeper is a notoriously cool character but he and his City team-mates were just too laid back on the day and were ultimately punished, allowing United to record a Premier League double over them for the first time in 10 years courtesy of a fully deserved 2-0 win.
Ederson was culpable for both goals, letting Anthony Martial’s weak volley slip through his fingers 30 minutes in and then tossing the ball away to Scott McTominay for his injury-time strike.
He also let one backpass carelessly roll under his foot and had to scramble back to clear off the line.
United were desperate for the victory that keeps alive their hopes of sneaking into the top four and securing a return to Champions League football, while City were strangely subdued during a first-half performance that fell far below Guardiola's high standards.
The visitors are still on course to finish as this season's runners-up but the Premier League is the least of their priorities, with runaway leaders Liverpool having long since disappeared over the horizon, leaving City to focus on what would be a remarkable cup treble.
However, that was no excuse for such an insipid approach to the game. All Manchester derbies matter, irrespective of positions in the table. United have now won three this season – and there could even be another one to come in the FA Cup.
The City boss presumably reminded his players of that at half-time as they went from dormant to dominant, but they paid for their first-half sloppiness.
Guardiola wants his side to go into the big games with rhythm, knowing it’s dangerous to try to switch their best form on and off, which is why he we will be so frustrated by their lacklustre first half.
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City’s only derby victory this season came at Old Trafford came exactly two months ago when they blitzed the home side during an unstoppable 45 minutes of fast, free-flowing football.
The contrast with this outing couldn’t have been greater. This time around, City managed just one shot during the first half – their worst effort in the Premier League since the game against Liverpool at Anfield in October 2018.
Worryingly, it was United who had the one player capable of making things happen going forward: Bruno Fernandes.
It was his inventive free-kick which set up Martial’s volleyed opener – even if the City players were furious that he took a dive to win it.
City could have few complaints about the final scoreline, though, as they struggled to combat United in midfield, with Fernandes’ creativity matched by the energy of Fred and Nemanja Matic behind him.
Of course, City’s main playmaker, Kevin De Bruyne, didn’t make Guardiola’s squad and his drive was missed. The Belgian has a sore shoulder and with a Champions League last-16 second leg against Real Madrid to come, it was decided not to risk him.
Phil Foden, who was dangerous from right wing in the Carabao Cup victory over Aston Villa a week, struggled to be as effective in his all-Mancunian battle with Brandon Williams, while the no-nonsense Aaron Wan-Bissaka effectively shut down the influence of Raheem Sterling on the opposite flank.
At least Sergio Aguero looked like he was desperate to set yet another record, with the Argentine three goals away from becoming the greatest derby goalscorer of all time for either side.
He robbed Luke Shaw to create City’s only real chance in the first half, for Raheem Sterling, and had the ball in the back the net just after the break only the goal to be disallowed for a marginal offside.
Sterling and Foden both went close to equalisers towards the end but another blank in front of goal, coupled with Ederson's errors, cost City dearly.
Obviously, this derby defeat won't hurt City's Premier League position. But a similarly insipid start against Madrid could leave their Champions League dream in tatters.