Birmingham had seemed set to move clear of the English Premiership drop zone after Sebastian Larsson netted midway through the second half.
But with two minutes left, Rams’ substitute Emmanuel Villa sent a header inside the far post to give Derby a flickering hope.
Indeed, Giles Barnes almost won it at the death, but Birmingham keeper Maik Taylor saved astutely.
Derby had a narrow escape on 37 minutes when new Birmingham striker James McFadden chipped in a ball which found Garry O’Connor, who bundled home only to be ruled offside.
The Blues were looking to leapfrog Reading and Bolton at the wrong end of the table, while Derby still look as good as down after just one win all season.
With Wigan winning at home to West Ham, Birmingham dropped into the bottom three on 21 points from 25 games, while Derby are 14 points from safety.
The Rams, under former Wigan boss Paul Jewell, recruited busily during the transfer window and former Manchester United keeper Roy Carroll did his best to keep the Birmingham attack at bay as former Blues man Robbie Savage battled in midfield and ex-Everton veteran defender Alan Stubbs made his bow.
Derby withdrew French winger Laurent Robert and Rob Earnshaw on the hour with Villa and Barnes coming on but Larsson promptly broke the deadlock, slamming in after an initial header from a David Murphy corner was blocked.
The Swedish scorer had to go off almost immediately afterwards, giving way to Argentine youngster Mauro Zarate.
Alex McLeish’s Birmingham are now in a huge dogfight having followed up a useful draw at Arsenal with three defeats.
As for Derby, survival seems a pipedream regardless of the arrival of new US owners General Sports and Entertainment.