When playing press conference bingo at any Manchester United preview, there will only ever be one winner. Whoever it is that draws the word "challenge" will be laughing. You can guarantee Sir Alex Ferguson will use it, usually in his opening sentence.
"Challenge" is not only Fergie's favourite word, it is his favourite concept. Facing up to the test - that is what has always got him out of bed in the morning. Whether it be out-flanking the Old Firm, knocking Liverpool off their perch, bettering the continental sophisticate Wenger, or out-pacing the clever young upstart Mourinho, the urge to take and pass an examination has long driven him. It is how he sees the world: one big obstacle to be overcome, one big doubter to be proved wrong.
It is also how he motivates his teams: are you up to the test? Can you show them? And he recognises that he now faces his toughest ever challenge. As he approaches his 40th year in management, he appreciates that Manchester City are the biggest rival to his hegemony he has encountered. To use another of his favourite phrases: 'there's no question about that'.
What City did last May was demonstrate that they had wherewithal to go with the money. When Sergio Aguero hit that winner against Queen's Park Rangers, three decades of comedy shackles were removed. Now they had the belief to sit with the cash.
City are not only the best resourced club in the history of the game, as a squad they are among the best organised. Plus, their owners have yet to demonstrate the kind of quixotic hiring and firing which has fundamentally undermined Chelsea's once assumed fitness for long-term supremacy.
Sure, City may not have sparkled this season in quite the same way they did last autumn, when they eviscerated United at Old Trafford. Sure, they may have folded lamely and tamely in the Champions League. Sure, the noises coming out of the dressing room are more and more interpreted as dissent. But domestically they look stronger and more solid than ever.
Boasting the most parsimonious defence in the league, they remain not only undefeated, but seemingly untouchable. The Etihad — currently at the centre of the most ambitious building project in British football — has not been breached in over two seasons. It is 40 matches since David Moyes's Everton were the last to inflict defeat on the home side. Once disparaged as the council house, Manchester's publicly funded stadium has become a fortress.
For Ferguson, Sunday's game has huge significance. He knows that one game does not make a season. With his team topping the division by three points, defeat will not be terminal. But he understands the symbolism. He appreciates that a victory for his side on Sunday would be worth far more than three points: it could represent the first hole in the City monolith.
A pity for him, then, that his chances of success have been so compromised. Last Saturday, he likened his team's defending at Reading to Cartoon Cavalcade. It is unlikely to get much better on Sunday.
There have been many theories as to why his back line has been so porous this season. Inconsistency of selection, chopping and changing goalkeepers, a frailty at full back: all are undoubtedly contributing factors. But Alan Hansen got it spot on when he said that were Ferguson able to field the Rio Ferdinand/Nemanja Vidic centre back combination of five seasons ago, all of his problems would be immediately rectified. Unfortunately he can't.
Vidic, the biggest loss in his armoury, he says has "no chance" of playing. Well, Ferguson has misled us about selection before. But even if he were able to name the Serb, after eight weeks on the sidelines, even a defender as substantial as him would struggle against an attack as potent as City's.
But all season, despite a defence leaking like a government department in the Thick of It, United have thrilled their supporters with an ability to out-score their opponents. Time and again the fight back has been stirring.
On Sunday, however, Ferguson's room for retaliation is compromised by his lack of midfield options. Anderson, Cleverley, Valencia and Nani are all likely to be out injured. Which not only deprives him of width, but also means that — in a choice between the venerable quartet of Fletcher, Carrick, Giggs and Scholes — he is entirely without midfield pace or penetration.
Still, up front he has Rooney, Hernandez and the man City most covet — Robin van Persie. They could yet spring a surprise, however. You never know: they could rise to Sunday's challenge.
Not that City will be going away, even if unlikely victory is secured. Now that Chelsea have self-destructed; now that Arsenal apparently believe fourth is enough and Tottenham have yet to find any proper consistency; the battle for the Premier League title this season is a simple one. It is a crosstown rivalry. Whatever happens on Sunday, the challenge remains.