The misery at Old Trafford after the game against Brighton was palpable. Perhaps as palpable as it's ever been since Sir Alex Ferguson's departure. United had just crashed out of the FA Cup in the third round with a feeble performance, leaving United with no silverware left to hunt in the rest of the season.
Any optimism was punctured with that full time whistle. There was nothing left to root for. United will trudge through the remainder of the season while our rivals take on European giants in the Champions League or trips to Wembley in the cup. United's season, in one game, became a right-off, for the second successive year.
Michael Carrick's appointment brought a little optimism back. Carrick is deeply embedded in United's culture and history. He was the backbone of one of Man United's greatest ever sides. Maybe he can get the Stretford End believing again. No one expected that to happen quite so quickly, and quite so conclusively.
Michael Carrick has already got United fans believing again after derby day delight
The transformation of Man United's team between the loss to Brighton and the derby day victory is almost unbelievable. United's win over Manchester City was not just a victory, it was an annihilation. It was one of United's best all-round performances in years. Had United had more luck, and a few less offsides, the score line could've been 5 or 6-0.
All the storylines that have haunted United in the past seemed to resolve themselves over 90 minutes. Kobbie Mainoo, who has struggled for minutes all season and seemed on the verge of leaving, played 90 minutes and controlled the midfield. Patrick Dorgu, who Ruben Amorim had thrown under the bus not two months ago, came to life on the wing and grabbed the second goal.
The change in mood was enough to cause whiplash. Defeating Man City in any scenario is cause for celebration on the red side of Manchester, but to do it in such a conclusive way, after a string of terrible performances, was almost absurd.
Some of this change in fortunes can be attributed to the so-called 'new manager bounce', a well-known phenomenon where teams make immediate gains following the sacking of a flailing manager. But Darren Fletcher wasn't able to get the team moving after Amorim's departure. Carrick was.
The mood around a club is more important than most fans realise. Pressure was high under Amorim; results were expected to improve, and with every passing week they didn't, the pressure grew, and the mood soured. United's victory over City has earned Carrick a clean slate.
Optimism is suddenly high around Old Trafford. Now that United have defeated City, could they defeat Arsenal next weekend? Is a Champions League place on the cards? Carrick has a whole host of new problems and expectations to deal with now that he has proven that his team can battle the best and win.
Whatever happens, Carrick has brought optimism back to Man United. The mood shift in Manchester has been dizzying, and Carrick has suddenly landed himself with high expectations, but stakes are largely low for the rest of the season. He has proved this team can work against one of the best teams in the world. He need only build on what he's already achieved in one game.