Seldom has the old 'master versus apprentice' cliché felt more relevant than at Wembley on Saturday night when Mikel Arteta out-thought his mentor on a potentially seismic day for his Arsenal rebuilding project.
It must be a strange experience for Pep Guardiola to leave with the sense that he was strategically inferior to an opponent, and stranger still when that opponent is his close friend and former colleague.
When it was put to Guardiola after the 2-0 FA Cup semi-final defeat that Arteta clearly learnt well during their time together at City, he flipped the dynamic on its head. "Maybe we learned from him," the City boss said, later adding that he did not think the game was lost because of "tactics", although no observer could claim that Arteta's game plan was ineffective. For their part, City were hardly brimming with ideas. In Guardiola's eyes, the defeat was the result of a mentality issue.
"In the first half we were not there. We were not ready for a semi-final of the FA Cup. We have to play the whole 90 minutes and we played just 45.
"In the first half everything was sloppy and not the right speed for this kind of game, when you want to reach the final."
City midfielder Ilkay Gundogan went as far as to say that "Arsenal wanted it more", which is a damning assessment of his team's mental approach.
City know that a repeat performance against Real Madrid in the Champions League would end their hopes of European glory. Guardiola's challenge is to find a solution to these psychological struggles.
"We have two more league games to play and then we have a big game against Madrid," said Gundogan.
"We should definitely improve because the way we played will not be enough to go into the next round of the Champions League. We have to improve quite quickly because we don't have much time."
Questions linger over City's defenders, who were so ruthlessly exposed by Pierre-Emerick Aubameyang. Eric Garcia, 19, clearly has talent, but remains inexperienced. John Stones and Nicolas Otamendi are not trusted in the bigger games. Both of Arsenal's goals came down Kyle Walker's side and Benjamin Mendy offered little in either half.
It is no wonder that Guardiola is still looking for a centre-back and left-back.
"I am not thinking about next season," said Guardiola. "We had two titles to fight for. On Saturday we lost one, but we have another one and once we finish we will be able to think about the team."
At Arsenal, Arteta and the club's executives have already given plenty of thought to recruitment. Their finances depend on whether they qualify for next season's Europa League, which would be secured if they win the FA Cup. In the space of a few days they have beaten Liverpool and City, and the task for Arteta is to now ensure they are able to produce these performances on a weekly basis.
"That is the challenge," he said. "The challenge is to do that for long periods in a season. From now we have a challenge, after a beautiful week winning against the best two teams in Europe, in my opinion. How do we react? Do we back off? Or do we go again?"
The spirited defensive showings against Liverpool and City have long felt beyond the modern Arsenal. Both David Luiz and Kieran Tierney were sensational in defence, while Granit Xhaka was their chief organiser in midfield.
"Every game has a different plan," said Arteta. "We have to be very analytical and realistic with our options, where they are and how we can make them better.
"The resilience we showed at the back was enormous and the efficiency up top, because you need that."
© Daily Telegraph, London