Dougie Freedman shuffled his pack from Saturday's victory at Queens Park Rangers, making use of the increased options available to him following Forest's transfer window dealings.
And it was one of the players brought back into the starting line-up, striker Dexter Blackstock, who netted the only goal of the game at St Andrew's in the 54th minute.
Line-ups and Text Commentary as it happened
Previously unbeaten Birmingham could have no complaints about their first reverse of the campaign as they struggled to cause problems for the Forest defence.
Gary Rowett's side threw everything into their search for an equaliser but goalkeeper Dorus de Vries was as good as his word in making up for the error that allowed Charlie Austin to open the goalscoring for QPR on Saturday.
The Reds return to the City Ground at the weekend for another live TV clash as high-flying Middlesbrough are the Saturday lunchtime visitors and what a difference to the atmosphere it will make for Forest to go into the game on the back of two excellent away wins.
Reaction: Dougie Freedman was a happy man afterwards, saying: "In the end I don't think Birmingham can complain about the result.
"Over 95 minutes we only gave them one chance and we deserved to win the game."
Opposite number Gary Rowett commented: "Forest set up to frustrate us and block us out of the game. They used Henri Lansbury in front of the back four in a destructive role which I thought he played really well.
"Sometimes you have to hold up your hands. The most disappointing thing for me was the way we tried to chase the game in the second half.
"We became a little frantic and a little bit too hurried and desperate on the ball and did not show enough quality."