Toure flourishes under new freedom as Fellaini fails badly to make any impact
Such things as this can happen between these teams and signify nothing. Alex Ferguson acknowledged after his club took their 20th title last April that Manchester City were capable of inflicting defeat upon his own.
It was just "in the rest of the games" United were far better. "Yes," Ferguson declared. "We are better than Man City at beating other teams. . ."
Time will tell, though the manner of Manchester United's unravelling – a story of rapier pace and menace versus sterility and labour – can be distilled down to the narrative of two players.
Yaya Toure and Marouane Fellaini occupy the same landscape in so very many ways – the central spaces, the transfer fees, the height.
But when you watched and winced for David Moyes' new £27.5m signing, chasing Jesus Navas across the sun-dappled turf a little after 5pm yesterday, arms pumping like pistons but legs not responding, you wondered how he could conceivably have cost his club £3m more than Toure did City.
"The superior player for a similar fee," is how Graeme Souness compared the two today, in a piece of analysis which now sounds terribly generous.
Fellaini's discussion, a few weeks ago, of how he did not fear occupying the space Roy Keane once took came in response to questions and was not him volunteering the name, though this took us so far from Keane's days that you almost gave thanks that an ITV studio was not overlooking this.
Fellaini (below) had given up the ghost by the time Navas crossed for Sergio Aguero to unravel the volley which sent City 4-0 up.
He was equally conspicuous by his absence in United's area – ducking and visibly wincing under the advancing army of blue as Alvaro Negredo found the header from a Samir Nasri corner which sent the ball scudding in off Toure's knee to send City 2-0 ahead.
Others in red delivered less than Fellaini in a performance which was more dismal than the 6-1 Old Trafford defeat of two years ago – a scoreline exaggerated by Ferguson's players ambitiously advancing to chase a losing cause.
You wondered, when you watched Ashley Young squander the ball to allow City's counter-attacking fourth, how he can find a way back. But these 90 minutes pose the question of what Fellaini will do for others.
"He'll help our great players get better by giving them more freedom," Moyes said a few weeks back.
If the vision was of Michael Carrick advancing to display more ambition and range then it was a forlorn hope.
Both Moyes' holding players were reduced to short, squat, square passes.
It was for Wayne Rooney, chief cook, bottlewasher and the only player worthy of the name 'champion', to drift back to do the job that Ander Herrera would have done had United only signed him from Athletic Bilbao on transfer deadline night.
The extra £6m which Moyes deemed too great that night would have looked like peanuts for a midfield player capable of liberating United from this.
And with every passing moment of Fellaini's struggle, Toure looked like a player for whom Barcelona had got the digits mixed up when they sold him for £24m. He is advancing forward far earlier, in a way that we did not see before Roberto Mancini left the building and Fernandinho walked in, and looks like a 15-goal a season player because of it.
There have been six in each of his last two seasons. Yesterday's poke was his fourth.
He took 50 seconds to display his brooding intent, barging in between Rooney and Fellaini with his head. And then there was the pace, the touch, the two great feet and the qualities of a juggernaut. Toure is utterly impossible to dislodge when he has the ball at his feet and is running.
A minor cameo on the penalty area 'D' with City already a goal ahead tells the story. Toure took the ball on his right instep, flipped it up and laid back for a speculative shot which went astray. Are there any other 6ft 4in players in football capable of a pass so cute as that?
The contribution of Vincent Kompany was, if anything, even greater – perverse though it may sound for a game dominated so entirely by City's offensive players.
The way he dislodged Rooney's head protector in the first half was accidental though entirely symbolic. He hustled Rooney, watched him get booked and was then City's quiet creator as they purred into top gear.
Kompany's part in the fourth – delivering the first pass, and progressing on the forward run to take out the defenders who were tracking back – was just one contribution.
Samir Nasri is also liberated from the torture of playing for Mancini, as his role in the first goal revealed: half a dozen rapid touches, Nasri nudging the ball this way and that, rolling it under his studs and flicking it with his instep for Aleksandar Kolarov to spear the cross which Aguero volleyed in.
But the abiding image was Fellaini, passing the ball straight to Toure in the game's 78th minute and allowing him again to fire the counter-attacking engine which saw Edin Dzeko, a substitute, to level the shot which David de Gea almost conspired to fumble over his line.
"Very good," his manager Manuel Pellegrini said of his display – a grey word for a performance which wrote colour across the day. (© Independent News Service)