City, who lost their unbeaten home league record to Nottingham Forest last weekend courtesy of a first defeat in 16 matches in all competitions, appeared destined to get back on track.
Just 24 hours after they were slapped with a transfer embargo by the Football League for failing to file their accounts in time, two of five signings made in the last 10 days shone to seemingly put the hosts in a winning position at St Andrew's.
The impressive Andros Townsend saw his 19th-minute shot converted by fellow loanee Erik Huseklepp from close range, before the Spurs winger's dazzling run set up a second-half strike for Marlon King.
But Derby, winless in six going into the game and without even a goal in their previous four, staged a remarkable comeback thanks to two in five minutes from recalled pair Steven Davies and Theo Robinson.
Davies was making his first start since suffering a fractured skull in October, but it was leading goalscorer Robinson who saw a shot deflected wide after just 17 seconds.
Townsend forced a save from Frank Fielding at the other end and it was he who created the opener.
Derby's defence fell to sleep and the unmarked wide man received a short corner on the edge of the penalty area, with his shot deflected into the path of Huseklepp - who poked home from six yards.
The hosts enjoyed a comfortable opening half-hour without really turning it on, with the goal-shy Rams providing next to no threat to City goalkeeper Boaz Myhill.
Derby came into proceedings marginally more as a largely forgettable opening 45 minutes came to a close, Shaun Barker heading over from Paul Green's free-kick.
But it was Birmingham who came closest to a second as Huseklepp's glancing header came back off the crossbar amid a succession of corners.
The second half started as the first finished, with the home side denied a second.
Huseklepp saw his shot well parried by Fielding before Townsend's follow-up was blocked on the line by Gareth Roberts.
The lively Townsend was at the centre of things again in the 57th minute as his lengthy run ended with a fine pass to King, who converted past Fielding from 12 yards.
Rams boss Nigel Clough introduced Ben Davies in an attempt to turn things around and the midfielder's first contribution was an inch-perfect cross for an unmarked Steven Davies to head home.
Robinson completed the turnaround just five minutes later, finishing Green's pass from the right as Birmingham were punished for more slack defending.
Fit-again Blues midfielder Guirane N'Daw forced a super save from Fielding with a shot from distance as the hosts went in search of a winner.
And they almost clinched just that in injury time as Steven Caldwell saw his header cleared off the line.