Joe Hart admits he was kicking himself despite City's stunning derby victory at Old Trafford - because he let a goal slip past him in last Sunday's 6-1 triumph.
England keeper Hart has played a key role in the Blues' turbo-charged start to lead the Barclays Premier League by five points going into tomorrow's home game with Wolves.
But his prospective derby clean sheet was ruined when Darren Fletcher fired in a cracker to pull the score back to 3-1 before City piled on the agony in the closing minutes.
He said: "I was annoyed. You can get carried away with the result and the three points, but we let in a goal. It kills me to let one in, it kills all of us.
"I'm so angry because we've hammered teams and then we've let a stupid goal in. It's frustrating, and we're trying for perfection at the moment.
When we're on top I just watch the game - it's usually quite an interesting game, so I don't mind!
"I try and be there when I'm required. I have bits to do, other than that, I stay out of the way."
Hart, speaking at AFC Urmston Meadowside, where he opened a new Football Foundation-funded sports pavilion, has leaked only seven goals as City have blasted 33 in just nine games.
He added: "We're doing our jobs at the back, which is all we need to do with the attack we've got. We're happy to just go about our business unnoticed and let the lads up front score the goals.
"Wolves are going to be tough, they're struggling and need the points as much as we do. I grew up with Dave Edwards. He scored the winner against me last time at their place, but I hope he plays."
Hart was "delighted" to support the grassroots game. The pavilion, with a community room and six changing rooms for a club that runs 54 teams, received a £521,000 Football Foundation grant.
Funded by the Premier League, the FA and the Government (via Sport England), the Foundation - the nation's largest sports charity - has awarded grants worth £420 million since its launch in 2000.