That was before Frank Lampard buried a spectacular penalty to confirm Chelsea's victory against the odds. That was before Nemanja Vidic had been sent off, missing Sunday's visit to Liverpool. That was before Chelsea turned the title race around. Maybe not in their favour, but certainly in Arsenal's and, beyond that, who knows?
This was one of the matches of the season and may yet be a pivotal moment. And to think at half-time there was only one team in it: the eventual losers.
Take a bow: Rooney celebrates in front of the Chelsea supporters after scoring the game's first goal
The spirit of Chelsea's victory must have come from a truly special place because, until David Luiz equalised, it was all but invisible. Stamford Bridge had the atmosphere of a wake, and Manchester United the swagger of champions. They had taken the game to Chelsea and it had worked. Wayne Rooney scored a deserved goal and every attack threatened a second.
Ferguson had already decreed Chelsea out of the title race but this result would confirm it. Carlo Ancelotti would be left with only the Champions League to save his skin, and on this form it looked a more remote goal than ever; on this form, few would be tipping Chelsea to even be in the Champions League next season.
Yet in a week dominated by misfiring air rifles and allegations of brutality, here was a reminder of why so many remain in thrall to the sheer thrill of Premier League football, for all its faults. This was truly a stunning game, a brawling monster of a contest, a heavyweight title fight from the days when combatants slugged it out, rather than waited for the opponent to die of boredom.
Flare-up: United winger Nani squares up to Ivanovic in the first half
In the second half, Chelsea made the game a battle of wills and Manchester United were over-run. Maybe that is why Ferguson looked so startled. He thought he had the scrappers here, he thought he had the tough nuts. Yet as Chelsea grew in stature, so Paul Scholes and Michael Carrick faded. It still needed two strokes of good fortune to get Chelsea back in the game but that does not detract from the importance of this result or the determination on display.
The first significant event was that David Luiz stayed on the field after what was clearly a foul on Wayne Rooney, worthy of a second yellow card. It would not have been enough to prevent Luiz scoring - that horse had bolted - but it would have rattled Chelsea and stopped their attacking impetus.
The biggest break, though, was that referee Martin Atkinson gave his 11th penalty of the season when to most eyes it looked as if Manchester United defender Chris Smalling simply could not get out of the path of the onrushing Yury Zhirkov. It was at that point that the roof fell in on Ferguson and the unlikeliest revival became a reality.
Heaven sent: David Luiz (centre) points to the skies after his equaliser
With a return at Old Trafford to come, Chelsea may decide the destination of the league title, even if it is not to remain in west London.
Earlier, it was Ancelotti who appeared to be suffering a thousand agonies. As the ball was fed out to Patrice Evra once more, and nobody covered him, the Chelsea manager threw his hands in the air despairingly. It made no difference. It happened just the same the next time and Ancelotti looked in disbelief at his staff on the bench as, inch by inch, Chelsea's season slipped away. How could they, he seemed to be saying. How could they be so careless?
United's goal, for which Rooney was left in space which, considering the area, must have a market value measured in millions, was further proof of a sloppiness that was simply not present in the Jose Mourinho era.
The Special One would have eviscerated the players who failed to close down Rooney; maybe Ancelotti did, too. Behind that genial facade is a man fighting for his career and, to a lesser extent, his reputation. He does not want to go from Double winner to fifth place in the space of a year. Certainly, Chelsea emerged for the second half with renewed purpose.
On the spot: Van der Sar watches helplessly as Lampard's penalty sails over his head
From a stroke of luck to a stroke of genius in one stride, and the signing of centre-back Luiz is already looking to be one of the most incisive moves of the season. That he should get on the score sheet before Fernando Torres will be taken by some as a negative, but Luiz's form has been the real positive for Chelsea over of the last month.
Here he finished with tremendous skill and certainty; had Torres replicated the moment, onlookers would have purred and considered him to be justifying his ?50million transfer fee. It was a classy goal, the most impressive strike of the night, although Frank Lampard's penalty also went in as if jet-propelled.
The goals typified the power of Chelsea's second-half performance, a certainty that was missing from their early play. Indeed, the performance posed as many questions as it provided answers. Optimists will now feverishly picture retaining the title in astonishing circumstances, yet equally qualification for the Champions League next season is far from guaranteed. It will depend which Chelsea turns up.
Their fading fortunes were distilled in 90 minutes here. There were strong reminders of the capability of this team, yet they were also at times sloppy, slow to get forward and aimless. They exploded into life only having given Manchester United a head start and while, at their best, they looked a match for anybody, at their worst, they reminded one of those dull Italian sides, easily dismissed by spirited Englishmen. They displayed incredible potential, but also the potential to disappoint.
Seeing red: referee Martin Atkinson (centre) sends Nemanja Vidic (right) off
Early on, gallows humour took the place of raw energy. 'Shoooot,' the crowd cried when Ashley Cole got the ball but the team, like Cole's cursed air rifle, misfired haplessly.
Ancelotti, hands plunged deep into the pockets of his tailored rain coat, looked on ashen-faced, much as he had appeared on Monday when trying to convince a sceptical world of the good in the trigger happy Cole. By the end, the roles were reversed, the season perhaps turned on its head, Ferguson a picture of impotent frustration, his captain gone for one match at least, Evra limping off injured.
This was a game Chelsea had to win, and they did, preserving their season in the process. They turned it around when all seemed lost, and maybe the season will turn, too. Game on, as they say. Maybe not for Chelsea, but for someone.
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