Maurizio Sarri's tactical masterclass was undermined by the shameful actions of Chelsea's record signing Kepa Arrizabalaga, who refused to leave the pitch in the closing minutes of extra time in order to be substituted.
Willy Caballero was left waiting on the touchline by an act of rebellion from the £71 million goalkeeper, who didn't allow the penalty specialist on the field despite suffering from an injury to his hamstring.
With the scores level at 0-0, Sarri was left furious and had to be held back by Antonio Rudiger after the match, such was his anger.
Ironically, Kepa also turned out to be a villain in the shootout itself. Despite making one save from Leroy Sane, he let a weak Sergio Aguero shot slip underneath him.
Raheem Sterling would then win the penalty shootout for City after Jorginho and David Luiz missed before him.
The mild-mannered Basque goalkeeper is known by his previous coaches for his professionalism, but there is unlikely to be any ramifications for him after a shambles was played out on the pitch.
Sarri described the situation as a "misunderstanding," though he admitted that it wasn't happy with the goalkeeper's conduct and plans to talk with him further about it this week.
Chelsea had put in a brilliant performance at Wembley to stem a recent run of bad form, with a 6-0 defeat to Manchester City still fresh in the minds of the players.
Pride was set to be restored after that worst defeat in 28 years, but the incident at the end of extra time ensured a negative feeling lingers on around the club ahead of Wednesday’s Premier League game against Tottenham Hotspur.
The under-fire Sarri lost control on Sunday evening, but the images played out across the world will continue to look ugly after this public row as pundits line up to criticise the goalkeeper.
“Kepa should never play for Chelsea again. That should be his last performance in a Chelsea shirt. He's a disgrace. I've never seen anything like it,” former Chelsea striker Chris Sutton roared on BBC Sport.
“If I was Sarri I would walk. You cannot be undermined. Why weren't the players dragging Kepa off anyway? Kepa should be sacked, not Sarri.”
That seems unlikely, though, due to the cost invested in the player and because of Chelsea’s recent transfer ban. However, this incident – which wouldn’t be out of place in a soap opera - only goes to embarrass the club even further.
“Once your number goes up you have to come off and show a bit of respect,” said the former Chelsea captain John Terry on SkySports, as the misunderstading leaves those involved red faced.
Chelsea’s performance deserves to be celebrated, as spectacular displays from Eden Hazard and N'Golo Kante lit up the Wembley showpiece. Unfortunately, all the talk will now be about yet another shambolic moment at the Stamford Bridge club.