Alex McLeish says Liam Ridgewell knew he had made a big mistake which led to David Hoilett's equaliser in the 1-1 draw with Blackburn.
The defender was caught on the ball when he seemed to be distracted as fellow team-mate Roger Johnson came back on to the field following treatment for a head injury.
That costly error was capitalised on by the vibrant Hoilett who nicked the ball from Ridgewell's toes and rounded Ben Foster to cancel out Lee Bowyer's earlier strike.
However, McLeish felt Ridgewell made up for his error in a solid second half which saw both sides struggle to break down two resilient defences.
"Roger ran on at the time when the ball was passed back to Ridgewell, I don't know if Ridgewell saw Roger out the corner of his eye but he should just have dealt with it," the Scot told Sky Sports.
"Going into the last minute or two of the first-half, he should just help it on, he's got to help it on into the Blackburn half and not take any chances but you know Liam's made a mistake.
"The next thing for Liam is to test his character and to see if he's got the bottle to do it the second-half and stand up to the task and he's done that.
"His second-half performance was strong. He knows he made a big mistake, he knows we can't afford to do that at this stage of the season especially when you're in the lower half of the table."
McLeish said his players have responded well to a tense atmosphere caused by City's position of 15th in the Premier League table which sees them hovering above the relegation zone.
However he could not have asked for a better first 45 and believes the next fixtures will have to be played "like cup finals".
"You could feel it, the tension, but the players responded extremely well over the last two weeks to get four really good points which I think will be very significant come the end of the season," he said.
"I thought we were terrific, the first-half, I thought we played some good football and if we'd gone in 2-0 it would've probably have been deserved, Blackburn were always a big threat.
"We would've loved the three points but we go towards next week's home game against Sunderland with great optimism.
"We've got home games coming up and they're going to be like cup finals."
Scores of Rovers fans appealed for City's opener to be disallowed for offside, however McLeish feels the clipped ball Cameron Jerome played was not a forward pass as Bowyer converted from close range.
He said: "You can understand why the home team would feel aggrieved but if you saw right down it seems that when Cameron squares it, Bowyer is square of him, he's not passed the ball forward.
Despite stalwart Johnson going off eventually with a head injury and Barry Ferguson getting an arm in the face, the Blues boss expects them to be back in contention for the game against the Black Cats.