They suffered two late scares after Kevin Campbell's eighth goal of the season in the 17th minute put them in charge.
First, Blues' Michael Johnson - a Forest fan and on as substitute for Martin Grainger - lashed the ball in at the far post from a Jonathon Bass cross with seven minutes left.
But Birmingham celebrations were cut short when referee Paul Danson ruled it out for a holding down offence by Paul Furlong.
Then evergreen Tony Cottee, on loan from Leicester, just failed to connect with a replica cross from Bass as Trevor Francis's side went all out for an equaliser. Forest boss Dave Bassett said: "It was a real battle - a very hard game for us.
"I thought Birmingham played well. They made it very difficult. They don't concede a lot of goals and it was a joy to see Kevin's go in.
"We've had a bad week with injuries and players going away, and it's a relief to get the win.
"There's very little to choose between the bottom eight in the Premier League and the top eight in our division. The good thing is that we are capable of playing better than this." Said Francis: "We deserved a draw. It's important we keep our spirits up and believe in what we are trying to do.
"We can't keep coming off after 90 minutes of full blooded effort like that and have nothing to show for it.
"Everyone goes away from a football match thinking about the result and not the performance, but we have to be happy with that performance."
Steve Bruce was once again missing from a Birmingham away line up and Francis said: "I decided because of an accumulation of games that I have to use Steve sparingly, but I felt that against the pace of Campbell, Darren Wassall was the right choice."
Only five wins in 18 games have put a question mark over Francis's future - but he said: "If there is any pressure on me then I am certainly not feeling it."
Scot Gemmill was a shining light in midfield for Forest, running the show with some excellent distribution and deftness of touch.
Steve Stone tended to run into pockets, but he was the provider as Campbell beat keeper Ian Bennett to the chase, stuck out a leg and watched gleefully as the ball rolled in.
Ian Woan nearly wrapped it up for Forest before their late shocks when, with his first touch after coming on as substitute, he sent a rocket left- footer inches wide.
FOREST 1 BIRMINGHAM 0
FOREST.- Beasant 7; Lyttle 7, Rogers 6 (Armstrong 6), Cooper 7, Chettle 7, Hjelve 6, Stone 6, GEMMILL 8, Van Hooijdonk 6, Campbell 7, Bart-Williams 7 (Woan 6).
BIRMINGHAM.- Bennett 7; Bass 6, Grainger 6 (Johnson 6), Wassall 6, Ablett 7, Marsden 7, Devlin 6 (Cottee 6), Robinson 7, Furlong 6, McCarthy 7, O'Connor 6 (Hughes 6).