Leon Osman's last-minute goal rescued a point for George Burley's side just as Cardiff were preparing to celebrate the revival of their promotion challenge at Pride Park.
Two goals in the space of a minute by Rob Earnshaw and Graham Kavanagh had overturned Ian Taylor's opener for the home side, for whom a week which revealed the full cost of relegation from the Premiership two years ago appeared to be ending with the trapdoor to the Second Division opening a little wider.
Cardiff still have their sights on going up, or at least reaching the play-offs, and were under orders to arrest a mid-season slump that had seen them take only six points in seven matches.
They looked to have done that only to leave the 5ft 8in Osman unmarked on the far post to head home substitute Richard Jackson's cross and restrict them to a point. It was the 22-year-old Osman's first goal in his third appearance after joining Derby on a month's loan from Everton.
"Sometimes I think we can get to the play-offs but other times, when we defend as ineptly as that, I think we'll never do it," Cardiff's manager, Lennie Lawrence, said.
The goal spared some embarrassment for the Pride Park board, who had predicted that Derby have enough resources to beat the drop, even as they revealed staggering losses of £27 million in the last two years. "We are very confident, as is the manager, that we have a squad capable of taking us away from the relegation zone," director Steve Harding had said.
It did not look that way, however, in an opening half in which only two good saves from Lee Grant, plus a goalline clearance by full-back Rob Edwards, denied Cardiff the upper hand. The goal by captain Taylor that put Derby ahead within four minutes of the restart came against the run of play, leaving Cardiff asking questions about their near-post defending of Candidio Costa's corner.
But the Welsh side drew level on the hour, Derby leaving Earnshaw onside when Peter Thorne headed down Richard Langley's cross. The Wales international stabbed the ball wide of Grant for his 23rd goal of the season.
Within 60 seconds, Cardiff were ahead. Paul Parry's cross from the left was headed away by Michael Johnson but only as far as Kavanagh, whose inspirational performance at the heart of midfield deserved some reward. The Cardiff captain's 20-yard shot gave Grant no chance, although a deflection helped it home.
With his side in control, Lawrence believed Cardiff should have made the points safe, and they surely would have had Earnshaw taken a good chance made by Rhys Weston, or Grant not pulled off another fine stop to deny substitute Alan Lee.
It was all the more disappointing for the Cardiff manager, then, that they should allow Derby's smallest player a free header. "If we end up missing out by a handful of points we'll rue today," Lawrence added.
"We had the chances to win 4-1 but until we learn to be ruthless we'll be stuck in mid-table."
Derby County 2
Taylor 49, Osman 90
Cardiff City 2
Earnshaw 60, Kavanagh 62
Half-time: 0-0 Attendance: 20,958