The Blues boss pinpointed Sergio Aguero’s early one-on-one with Asmir Begovic as the moment that he began to fear for his side after their humbling at the Etihad Stadium.

Jose Mourinho insists he knew Chelsea were in trouble just 10 seconds into their 3-0 drubbing at the hands of Premier League title rivals Manchester City.

Goals from Sergio Aguero, Vincent Kompany and Fernandinho saw off the Blues as Manuel Pellegrini’s men made a powerful early-season statement in their bid to claim a third league title in five years.

But Chelsea might have been dead and buried by half-time; Aguero missed several clear chances in the first 45 minutes including one in the opening moments when he raced onto a David Silva pass and fired a low shot against the shin of an onrushing Asmir Begovic.

Mourinho afterwards revealed this was the point at which he feared for his side and voiced his frustration at their uncharacteristically slack defending.

“When the game started and 10 seconds later you have Aguero behind the defensive line and facing Begovic, immediately you get the notion that the start wasn’t good,” the Chelsea boss told reporters. “After that he made two or three saves because of that fragility.

“I was the first one to be disappointed. All week you are speaking about movements, directions of the game, mechanisms, Aguero’s runs and Aguero’s positions, the wingers coming inside, and after 10 seconds Aguero is in the face of Begovic. We were defensively poor in the first half.”

Mourinho also elaborated on his surprising decision to substitute captain John Terry for tactical reasons at half-time as Chelsea pushed for an equaliser.

“The point was not to take John out it was to bring [Kurt] Zouma in – I wanted my fastest player on the pitch, not on the bench,’ he added. “It was clear for me that Zouma has to play. I had to bring one out and I brought out my captain. He was on the bench and still my captain because the armband is just the armband.

“I can tell you that he was not dancing in the dressing-room, and I can tell you also that he was not having a bad reaction. He did what everybody does. The manager says ‘this guy comes in and that guy goes out’, and they all do the same. They wait for the team to go out, they shower and change and go back to the bench.

“My decision was proven right because we controlled the depth of the game and the counter-attack totally. But John is a player with my entire confidence for sure. With me, he was never substituted but with other managers he was not even selected. He was not playing or people thought his career at Chelsea was over.

“I don’t know if you ask many questions to [Rafa] Benitez, [Andre] Villas-Boas, [Roberto] Di Matteo, the ones who never played him. I’m the one you shouldn’t ask because I’m the one who played him every game, made him captain and recovered him from a difficult situation with other managers.

“I’m the one who has the right to look at the game and to say I want Zouma on.”