First the victory and the vindication, then the historic humiliation. Arsene Wenger's has been a week of emotional extremes, with the resounding, remarkable Champions League win over Udinese followed by the embarrassing, execrable display of defending Old Trafford witnessed.
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Manchester United's great eight was Arsenal's new low, their biggest defeat since the 19th century.
A demolition job of a weakened team doubled up as an elegant evisceration of Wenger's ethos. His assortment of the untried proved unsuitable and unsuccessful in the extreme. The case to sign, to strengthen, to solidify has never been greater, the flaws in the theory of buying on the cheap and promoting from within never more evident.
A career-defining day for Wayne Rooney, who accelerated past 150 United goals with a hat-trick, for Ashley Young, who opened his account for his new club and, potentially, for David de Gea, whose penalty save from Robin van Persie was the first illustration of his ability in England, could have similar implications for the Arsenal underachievers.
Carl Jenkinson's journey from non-league to Premier League lasted less than a year. It was cruelly clear long before the right-back was expelled; tortured exquisitely by Young, he was out of position, outclassed and, eventually, out of the action after he was dismissed for two bookable offences.
On the other flank, Armand Traore may have been still worse. Yet individual failings were compounded by collective flaws. Neither was afforded any assistance, with Andrey Arshavin especially culpable in Traore's troubles. Arsenal are deemed Barcelona-like, but Pep Guardiola's side press with greater vigour than anyone else. Wenger's charges, in comparison, afforded United the freedom of Old Trafford.
It was compounded by poor planning. Operating with a high defensive line poses risks, even without factoring in the pace of the United front line and Arsenal's haphazard attempts to play offside. That contributed to three of the goals.
The quartet of Jenkinson, Johan Djourou, Laurent Koscielny and Traore were less a back four than a group of individuals floundering in isolation. The overall impression was one of astonishing naivety.
Without Thomas Vermaelen, Kieran Gibbs and Bacary Sagna, Arsenal's defence were short-staffed, but the understudies lacked the basic requirements. The staple diet of the senior professional's game - communication, leadership, organisation, resolve - were conspicuous by their absence.
And yet it is a question of authority as well as experience. While Arsene's ingenues were drowning, Fergie's Fledglings were surfing a wave of momentum. Like Arsenal's, United's starting 11 had an average age of 23. There, however, the similarities end. Players such as Phil Jones, however, have a presence that suggests they belong. Danny Welbeck and Tom Cleverley, recalled from loans and parachuted into the first team, are relishing the responsibility of starting, not shrinking from it.
Premier League in pictures
The best images from week 3 of the Premier League.
Above all, in Rooney, United have the Premier League's alpha male, a swaggering beast of a player with a lovely, delicate touch on free kicks. Two were planted in Wojciech Szczesny's top corner, from very different angles but with equal precision. He was rampant; Young, scorer of a long-range brace, little less dominant. The last reclaimed top position in the table from Manchester City. Beating Arsenal was once the be all and end all for United; now it is part of a wider picture
When harsh words and cold pizza were flung between the teams, vitriol came from Sir Alex Ferguson. Now there is pity and, while Wenger has an entente cordiale with his old adversary, and while Ferguson is an advocate of solidarity between managers, especially when they pose no threat to him, the Frenchman should be shrewd enough to recognise that rivals are not granted supportive statements.
Then again, immediate rivals are not beaten 8-2, not opened up repeatedly, not overwhelmed completely. It epitomised United's confidence when Rooney attempted to score from his own half. It highlighted Arsenal's helplessness when Chris Smalling was allowed to run 50 yards unchecked. It summed up the sense of confusion that Theo Walcott finished the game at right-back, and it hinted at United's dominance that they managed 28 attempts on the visitors' goal.
And yet for every image of astonishing superiority and crushing inferiority, none told the story as dramatically, as emphatically, as brutally as a glance at the scoreboard. Manchester United 8 Arsenal 2. Astonishing.
