Both are the best at what they do. The difference lies in the emphasis.
Jose Mourinho argued that David de Gea is the best in the world after he equalled a Premier League record by making 14 saves in the 3-1 win at Arsenal last week. A double stop from Alexandre Lacazette and Alexis Sanchez was especially impressive.
United have conceded the fewest goals in the division and De Gea has the most clean sheets, with a save completion rate of 86.1 per cent.
City’s Ederson, meanwhile, is the best on the ball. His 85.3 per cent pass completion rate shows his upbringing as an outfield player. “Modern football requires those skills because it’s changed,” he said.
Crucially, though, he has brought the reliability as a shot-stopper that Claudio Bravo lacked: the Chilean’s traumatic debut at Old Trafford last season was a sign of things to come.
However, his willingness to come out of his box to get the ball cost City a goal against Shakhtar Donetsk. It was his first major error.
Neither side is at full-strength. The fact they have the two best defensive records in the division shows it has scarcely mattered.
Indeed, the injured Eric Bailly and John Stones are arguably the finest centre-backs at each club. United may have Phil Jones back but Mourinho’s second-string unit of Marcos Rojo, Chris Smalling and Victor Lindelof, after a traumatic start to life at Old Trafford, performed well at Arsenal.
The Portuguese is likely to continue with a back three. Guardiola will play a pair: Nicolas Otamendi has made fewer errors this season but Vincent Kompany, long a derby hero, could be crucial in marking Romelu Lukaku and defending dead balls.
City have only really conceded from set-pieces – and United have a famously tall team – and against counter-attacks. United will field wing-backs, City full-backs who advance further, so there could be space behind them. All have an attacking edge.
United’s Ashley Young and Antonio Valencia are converted wingers. City’s Fabian Delph will come infield into midfield while Kyle Walker surges forward on the right.
One fundamental difference is City’s high defensive line, with Ederson often outside his box as he acts as a sweeper, while Mourinho prefers a low block, limiting space behind his centre-backs.
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A department that may be defined by an absence, but an area where the sides are separated by a gulf in philosophies.
Minus the suspended Paul Pogba, Mourinho should choose twin deep-lying defensive midfielders, in Ander Herrera and Nemanja Matic. The importance the Portuguese places on character was evident when he said the Serb was injured but would definitely play.
The problem is that Pogba, who got two assists before his dismissal at Arsenal last week, is irreplaceable as a bridge between defence and attack. United average 3.0 league goals per game when he starts and 1.57 when he does not. Marouane Fellaini could be a physical impact substitute.
A Mourinho favourite seems an anti-Guardiola player.
If United’s midfield is essentially destructive, City’s is constructive. United won at Arsenal with 25 per cent of possession. They had 31 per cent in the 0-0 at the Etihad last season.
City will field one defensive midfielder to United’s two, but will outnumber them with the two “free eights", as Kevin de Bruyne described the attack-minded pair. City are at their slickest when he, David Silva and Fernandinho form the central role.
They outclassed United at Old Trafford last season. It will be intriguing if Mourinho uses Jesse Lingard to pick up Fernandinho, who has played most passes in the Premier League this season.
Two different trios, but both bring great pace.
Mourinho's new-look attack of Lingard, Lukaku and Anthony Martial linked up well at Arsenal where Pogba supported them on speedy counter-attacks. Their movement off the ball was particularly important while Lukaku, after a barren run of 12 games that produced a solitary goal, scored in style against CSKA Moscow on Tuesday.
They can line up either with two men in wider roles or with Lingard behind twin strikers, and Martial and Lukaku are quicker than the City centre-backs.
In contrast, Pep Guardiola uses out-and-out wingers.
Leroy Sane and Raheem Sterling start wide, the German in particular, and come infield into the box, a policy that has worked so well that they have scored 21 times between them.
Sergio Aguero has scored four goals in three visits to Old Trafford but while United have seen him at his sharpest, City have not often of late.
Gabriel Jesus may be a likelier starter, but Guardiola has started to pair them in a 4-2-4 system when he goes for all-out attack in the closing stages of games.