Sergio Aguero has done some remarkable things since he arrived in Manchester as a £40m antidote to the surly self-absorption of Carlos Tevez.
A personal favourite is the goal he fashioned with Mario Balotelli at Stamford Bridge a few weeks ago. It had everything you wanted in a star footballer, vision, pace, fine skill and the most swaggering nerve. But then you only have to browse YouTube for a little while to be reminded that he has been achieving such levels of performance since he first won his place in the Independiente team as a 15-year-old. No wonder Diego Maradona's daughter Giannina turned her head.
Yet mere virtuosity has been known to conceal some quite serious flaws and when Aguero arrived at the Etihad Stadium there were some worries that his game of fine touch might be pummelled by the physical intensity of the Premier League.
He could hardly have looked better in his briefly delayed debut as a substitute against Swansea at the start of the season. Two goals, a brilliant assist for David Silva, brought instant enchantment. But would it last, would Andy Gray's fear for Lionel Messi on a rainy day at Stoke be quickly transferred to his glittering compatriot?
It seemed like a valid question – right up to his extraordinary weekend performance in a losing cause against Manchester United.
Roy Keane, the relentless pragmatist, sniffed at suggestions that City had scored a moral victory after going down to 10 men in 12 minutes. He said that the only thing that mattered was that United were going into the fourth-round draw.
But then not to Aguero, it seemed fair to say. What mattered to him was that he served his team with every scrap of the best of himself. He ran endlessly, he held together the wonderful certainties of his skill and judgement, and he scored the goal that might just have conjured one of the most extraordinary results in FA Cup history.
For some of us the 23-year-old Argentine also hardened the suspicion that his arrival at City signalled rather more than the acquisition of another expensive and undoubtedly gifted performer. It may have been a bit of a reach but that night against Swansea when he combined so exquisitely with Silva, when he released an attacking urge that was simply stunning, it seemed Manch-ester City's ambition might indeed be entering an entirely new phase.
How could the well developed defensive instincts of Roberto Mancini not finally yield to the reality of his new attacking force – and make preposterous the idea that he would ever again take a team to somewhere like Old Trafford or Stamford Bridge or the Emirates with no greater resolution than to put 10 men behind the ball.
If you were sceptical – and at times deeply so – about the ability of any club to pay so much, so quickly, to so many disparate characters and still expect some seamless progress towards a genuine team ethos, one fit to challenge at the highest level, you also had to acknowledge what might be a special quality in the young father of Maradona's grandchild.
On Sunday some of those suspicions fell into place. The better Aguero played, the more heart he displayed, the greater was the response of his colleagues. James Milner was especially impressive in the train of Aguero.
He looked like the player he was supposed to be when he first emerged at Leeds United, which is to say a teenager of resolution and authority along with impressive talent. On several occasions Milner drove at a faltering United with the conviction of someone who truly believed that an impossible result might just be achieved. It was a contagion of defiance, backed by a brilliant adjustment of tactics by Mancini, and might just have been the most significant passage of play since the birth of the Sheikh Mansour's "project".
Keane said that Mancini took away only a defeat but surely it wasn't so. The City manager, a football man not keen on making himself a captive of any kind of hubris, declared that yes, while playing like that with 10 men for most the game, City could indeed win the Premier League.
It was a brief departure from the manager's concern over the departure for Africa of Yaya Touré and Kolo Touré and the absence of Gareth Barry, Mario Balotelli and Eden Dzeko. But then it was surely justified and easily identified. It was the beautifully timed gift of Sergio Aguero.
Here goes nothing... I agree with Poll
As a fervent member of the campaign to bring referees into the same kind of performance requirements as most of the rest of humanity, I never expected to utter the following sentence.
I agree 100 per cent with Graham Poll.
There are times when the guru commentator on refereeing affairs puts the defence of his former workmates up there with the doctrine of Papal infallibility. Not, though, in the dismal case of Chris Foy whose reward for making a fiasco of the recent Stoke-Spurs game was to get Sunday's mega collision between Manchester City and United.
Not altogether surprisingly, he distorted the balance of the game hugely after just a few minutes. Some said that he was right to interpret Vincent Kompany's tackle on Nani as a reckless two-footed lunge, others thought he had completely misjudged the nature and the performance of a superb piece of defensive timing.
Poll's verdict: "You could argue that Kompany's tackle wasn't even a foul. If he [Foy] wanted to make his mark early in a derby game, then it was yellow at worst. This huge game was not a good day for the officials."
Wayne Rooney has also received some criticism for his ferocious agitation for the red card but of course this is just a part of today's game, a practice followed by so many, including the complaining City manager Roberto Mancini. It was, nonetheless, still despicable enough to make you sick.
Owners must pay bill to dine at top table
Neil Warnock might be excused a bitter aside when he picks up his pay-off from Queen's Park Rangers and examines a new notch on a glibly bestowed and decidedly unhelpful reputation.
Warnock, they say, is a dab hand at taking you to the stars but has more difficulty in staying up there in the Premier League.
There could be a compelling reason for this. It concerns the little matter of a workable budget. New owner Tony Fernandes put Warnock on warning a few days ago while at the same time making derisory offers for players who might have made Warnock feel a little less as though he was trying to climb Mount Blanc in threadbare carpet slippers.
Warnock's likely successor, Mark Hughes, was once asked the reason for not having Blackburn Rovers play more attractive football. "Not to put too fine a point on it," replied Hughes, "somewhere around 50m quid."
Khan should be grateful for second chance
Amir Khan isn't going to get an argument here by suggesting the man in the hat at the Washington DC ringside looked less a righteous official of the International Boxing Federation than a conspiracy keen to happen.
Much more contentious, though, is Khan's demand for a formal return of his World Championship belts.
The claim that Mustafa Ameen succeeded in interfering with the scoring that gave challenger Lamont Peterson a split decision would have a lot more credence if we had a case of burglary in the shadow of the White House.
Unfortunately for Khan, we don't. Peterson, especially given the American prejudice in favour of fighters who tend to go forward, was not so hard to identify as the winner. Khan should be happy to settle for a rematch and the chance to improve sharply a performance that made a mockery of some over-wrought claims on his behalf – not least the one that he is a contender for the title of world pound-for-pound champion.