Ferguson is congratulated after scoring Birmingham's winner
Birmingham progressed to the FA Cup fourth round courtesy of a narrow win over Nottingham Forest in a replay largely dominated by the visitors.
Barry Ferguson scored the only goal of the game on the hour, curling in after a one-two with Christian Benitez.
The goal was harsh on a Forest side who had dominated possession but wasted a host of chances to score.
They will rue Nathan Tyson's early miss and David McGoldrick's inability to beat keeper Joe Hart from close range.
Forest had already unlucky not to make it into the next round and a tie against Everton at Goodison Park at the first time of asking after Robert Earnshaw's penalty miss meant the original tie ended in a stalemate.
Earnshaw was denied the chance to make amends for his miss by a hamstring injury, and boss Billy Davies made seven changes from the side which beat West Brom 3-1 at the weekend, fulfilling his promise that the league remains his side's priority.
In contrast, Birmingham kept the same side which drew 1-1 with Manchester United on Saturday, a result which had extended their unbeaten run to 13 matches.
But the visitors made the more confident start, offering a clear indication of how Forest's success in the Championship has invigorated the entire squad.
Earnshaw's replacement Tyson could have given them the lead in the first minute but he put his header from a Dele Adebola cross wide.
Forest continued to fashion chances, with Luke Chambers and McGoldrick drawing relatively comfortable saves from home keeper Hart and Garath McCleary and Lewis McGugan shooting wide from long range.
Birmingham created comparatively little, with Sebastian Larsson and Benitez wasting their best chances by firing shots well off target from the edge of the box.
It was largely the performance of City's on-loan keeper Hart which denied Forest a deserved victory at the City Ground ten days ago.
Birmingham were again grateful to their highly-rated temporary acquisition late in the first half as he produced two good saves to keep his side on level terms.
Forest picked up where they had left off in the second half.
Twice in the first five minutes they flashed shots across goal with McGugan and Tyson guilty of lacking accuracy when well placed.
For all of their dominance, Forest's failing was their wastefulness which continued to leave the door open for Birmingham.
And Birmingham took advantage as they grabbed the lead when Ferguson played a one-two with Benitez before unleashing a superb curling shot into the bottom left corner of the goal to register his first goal in a Blues shirt.
It was an undeserved lead but the visitors had only themselves to blame.
The goal knocked Forest out of their stride but Birmingham regained their composure and seized greater control on the match.
They dominated possession and could have doubled their lead with a Roger Johnson header from a Larsson corner but Lee Camp was on hand to save.
Forest, though, are unbeaten away from home this season and headed into this game unbeaten in 18 matches and these were clearly not records they were willing to sacrifice easily.
Tyson had a glorious opportunity to get the visitors back on level terms when McGugan swung in an inch perfect cross but the striker scooped it over the bar.
The continued to push for an equaliser but Birmingham have proven themselves adept at holding on to single-goal leads this season and they were in no mood to allow the game to slip from their grasp.
They defended manfully and had Luke Chambers not cleared a Cameron Jerome effort off the line they could have given the scoreline a favourable look they barely deserved.
Below-par they may have been in front of a crowd of just over 9,000 but their unbeaten run continues.
Birmingham manager Alex McLeish:
"It was a struggle. We didn't play at our best tonight but the guys showed their resilience.
"Forest started well and had a go at us. They are a good team and they were a handful.
"Joe has got a good a chance as anyone of being England goalkeeper in the summer."
Nottingham Forest manager Billy Davies:
"We've now played Birmingham over two games and their goalkeeper has been the man of the match on both occasions.
"This was a big learning curve in terms of it being important to take your chances.
"I am very proud of the way the people we've put out on the pitch tonight performed and it was a great experience for them."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.