A last-minute equaliser from Leon Osman earned Derby a vital point and dented Cardiff's play-off hopes.
Osman was left unmarked in the 90th minute to head in from six yards just when Cardiff had looked to be heading for a deserved victory.
But the visitors only had themselves to blame for wasting the chances that would have put the game out of Derby's reach before Osman punished slack defending.
Cardiff manager Lennie Lawrence admitted: "We had the chances to make it three but failed to put the game beyond Derby and we paid the price." Derby showed the spirit they will need to get out of relegation trouble by battling to the end but Cardiff will wonder how they let this one slip away.
The quality of their midfield had Derby stretched in the second half but the finishing did not match the approach work and the Rams hung on to earn what could be a very vital point.
It looked as if it might have been even better for George Burley's side when Ian Taylor headed Derby into a 48th minute lead from a right-wing corner by Candido Costa.
Taylor headed wide in the first half but this time he made no mistake putting the ball into the top left corner from six yards out.
Cardiff responded impressively and, on the hour, Derby's defence paid the price for looking to the linesman.
Rob Earnshaw was onside when strike partner Peter Thorne headed the ball down and the Wales striker made no mistake by beating Lee Grant from close range.
Burley said later: "For some reason, we looked for offside which is not the way that we defend and that was poor." Derby could do little about Cardiff's second which was a 20-yard drive from midfielder Graham Kavanagh that took a slight deflection off Michael Johnson before finding the top left-hand corner.
Grant made a crucial save late on and Derby made that pay when Osman popped up to head in a right-wing cross.