Birmingham left with a Barclays Premier League point after holding out to repeat the 0-0 scoreline from the midweek derby, and although City remain fourth in the table there were boos from home fans.
There was also a howl of protest around the ground when manager Mancini withdrew skipper Carlos Tevez towards the end and replaced him with midfielder Gareth Barry as City battled to break Birmingham down.
But the Blues boss said: “We were pushing players into the box, and Carlos has had a little injury for two or three weeks. I thought that if I took him off and put on another player, there was a chance to score.
“Do you think that if I put on four strikers we will score four goals? That’s not football. All supporters are like this, here and in Italy. They think why not put on two, three, four, five strikers?
“If football was like that, I’d put ten strikers on the pitch! But it’s not. We had 17 chances. In the first half we played too slowly, but in the second we played good football but didn’t score. It happens.”
Mancini lost Emmanuel Adebayor with a heel injury in training, leaving Roque Santa Cruz and Jo to provide the attacking options on the City bench. He said: “I am also frustrated, because I want to win.
“The supporters are unhappy but we played 100 per cent and had a lot of chances to score. we have this problem, finding it difficult to score, but it is important that we did have the chances.
“We must improve on this - when we have a chance, we must score. If we don’t, then it is a problem. We’ve had this problem since the start of the season. If Carlos Tevez does not score a goal, we don’t have another player to score a goal. We had Balotelli injured and now banned, Adebayor injured, but we must continue to work.”
