Pep Guardiola highlighted Claudio Bravo's dismissal as the turning point in Manchester City's humbling on his return to Barcelona – but defended his philosophy concerning goalkeepers playing out from the back.
Trailing to Lionel Messi's opener, Chile international Bravo was shown a straight red card for deliberately handballing Luis Suarez's goal-bound shot, giving Barca the initiative in a game in which they had failed to hit their usual heights.
City continued to be architects of their own downfall as Messi punished errors to complete his hat-trick, before Neymar added gloss to the victory late on.
When asked about his philosophy on goalkeepers playing out from the back, Guardiola said: "There will be no change. It stays the same. I'm sorry, until the last day of my career as a coach I will try to play from our goalkeeper.
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"Sometimes there are mistakes and sometimes you have to kick the ball out but most of the time, when we play good, it starts from there."
He added: "It always difficult to play against Barcelona with 11 players so with 10 the game was over. Until then the game was open.
"The last time I was here [with Bayern] we controlled the game but didn't create any chances, today we created enough.
"We arrived at their by-line many times and we created enough chances to score one or two goals. When Barcelona's strikers arrive they punish you because they have a lot of quality but, with exception to the goal (Messi's first), we were in control.
"We have given opponents a lot; the start in Glasgow, the own goal at White Hart Lane and missed penalties [against Everton].
"But it's only October, we've lost a game, it's not quarter-finals so in two weeks we have one more game and, of course, we will have to win two games from three to quality for the last 16.
"We knew the group would be tough and now have to analyse what happened and rest for the next game against Southampton."
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Asked whether Wednesday's defeat was the worst defeat of his career, the City boss added: "No. [The worst] was at Real Madrid when I was at Bayern Munich. In that moment I didn't make the correct decisions.
"We lost 4-0 so yes, it is bad, but not given the club's situation. We are a new club, we are in the process of getting to know each other and we are a club who weren't in Europe for 35 years.
"We came here and played with huge personality, with good high pressing and dealt with long balls to Luis Suarez and Neymar, which is not easy.
"We kept the ball, we created clear chances and they scored through Fernandinho's slip. We started the second half really well and created chances with Kevin De Bruyne.
"Of course after that we played 10 against 11 against Barcelona and were soon 2-0 down."
City were left to rue a host of missed chances on a night where Barcelona were not at their scintillating best.
For the second game running, City were without talisman Sergio Aguero as Guardiola named the Argentine on the bench, a decision he revealed he made consciously.
"It was my decision [not to start Aguero]," Guardiola said. "He was OK (not injured).
"I wanted more players in that position and that was the reason why."