Man Utd v Man City: Jose Mourinho and Pep Guardiola Manchester rivalry is only getting started
Forget La Liga, the story of bosses' feud will be defined by Manchester chapter
Forget what has gone before. Lionel Messi cannot win today's Manchester derby for Pep Guardiola, just as Jose Mourinho cannot instruct Pepe and Sergio Ramos to light fires all over the pitch for Manchester United.
Two managers with a shared history and an enmity forged in Spain, but the reality of Mourinho versus Guardiola is that their rivalry will be defined by what happens in the next three years.
For football's two most celebrated and sought-after coaches, Manchester is where they are at and it is a wholly different landscape from that which they fought over in Spain with Real Madrid and Barcelona.
There is a temptation to view this rivalry through the prism of their previous encounters in La Liga, when Mourinho won just three of his 16 encounters with Guardiola's Barcelona.
History shapes the future and Guardiola's winning ratio will affect Mourinho just as Mourinho's psychological warfare will continue to gnaw away at Guardiola, but the past is another country.
United versus City is not Real versus Barca, and that is not to relegate Manchester's football rivalry to second-billing.
Had the two managers been taking charge of Celtic versus Rangers today, Mourinho and Guardiola would be involved in perhaps the closest comparison to the Real-Barcelona rivalry in world football - two clubs accustomed to a duopoly.
With United and City, however, both men must overcome the challenge of outsiders such as Chelsea, Liverpool and Arsenal, as much as each other.
And this is why the Manchester derby, and the two clubs' battle for supremacy, provides the perfect theatre in which to play out, and decide, the rivalry between Mourinho and Guardiola.
Guardiola cannot rely on the institutional power of Barcelona or Bayern Munich with City. He cannot turn to Messi, or expect to sweep aside all domestic rivals as he did with Bayern.
Mourinho, whose knowledge of the Premier League gives him an early advantage, also faces new challenges at Old Trafford, such as winning with a style that reflects United's history and tradition, but also restoring the sheen to a personal reputation that has been damaged and dulled by his swift and acrimonious fall from grace at Chelsea.
Guardiola must prove he can succeed without a rich inheritance at City and build a team to compare with those he walked into in Catalonia and Bavaria, but Mourinho must show he can still succeed and remind the world why he described himself as the Special One.
And they are on a level playing field in Manchester. Neither has a head start on the other.
Goal difference separated the two clubs when the curtain fell on the reigns of Manuel Pellegrini and Louis van Gaal at the end of last season.
Mourinho has dragged United out of their post-Sir Alex Ferguson slumber with an injection of charisma, certainty and the recruitment of Paul Pogba and Zlatan Ibrahimovic, while Guardiola has already imposed his personality on City with a £170m spending spree at the same time as re-writing the play-book at the Etihad.
Inverted full-backs, attacking centre-halves, the rehabilitation of Raheem Sterling and the cold, ruthless discarding of Joe Hart - make no mistake, this is already Guardiola's Manchester City.
And at Old Trafford, while proving more subtle in his tweaking, there have also been changes under Mourinho.
United have become a much more physically-imposing team - Ibrahimovic, Pogba, Marouane Fellaini and Eric Bailly threaten to dwarf their opponents on derby day - while the volume has also been turned up on the pitch.
Watch carefully today when a decision goes against United and how much more quickly the likes of Wayne Rooney, Juan Mata and Daley Blind will question the decisions of the officials.
Under Van Gaal, United were often too timid, but the fighting spirit of Mourinho's best teams is already beginning to emerge - a positive which risks becoming a negative if arguing the toss develops into referee-baiting.
But the two clubs are perfect for their respective managers, even if both have flirted with the other in the past. Guardiola for United and Mourinho for City would offer less to the men than their current roles, however.
Guardiola needs to prove he can build a team, and even a club, having succeeded with royalty at Barca and Bayern.
City can be Guardiola's blank canvas, potentially enabling him to create at the Etihad what Johan Cruyff built at Barcelona.
And Mourinho, a man whose stellar CV includes the majesty of Real and Inter Milan, can now get to work on the challenge of restoring United to the summit of the game and giving the club justification to boast that they can punch their weight on the pitch just as powerfully as off it.
For too long, United have declared themselves to be the biggest club in the world while Bayern, Real and Barca have simply got on with the business of winning.
Both clubs and both managers have lofty ambitions of domestic and global dominance, but you cannot be the biggest or the best if you cannot run your own neighbourhood.
So for Mourinho and Guardiola, their rivalry is now all about what happens on their own doorstep.
They might well be new neighbours on Coronation Street, arguing over the cobbles about the noise next door.
Welcome to Manchester, Jose and Pep.