Two goals from top-scorer Steven Howard and another for Giles Barnes cancelled out Paul Parry's first-half equaliser, although Cardiff will point to two vital decisions that turned the match.
Steven Thompson was adjudged to have handled for Derby's 28th minute penalty, although replays suggested he was unlucky and that the ball had struck him near the shoulder.
Cardiff were also convinced that Howard's second and Derby's third was offside and any chance they had of coming back from a two-goal deficit for the second time in five days disappeared when substitute Jason Byrne missed a sitter in the 71st minute.
Once again Derby were far from convincing especially in a first half which was largely controlled by Cardiff and the outcome might have been different if leading scorer Michael Chopra had not pulled a hamstring a minute after his team had drawn level.
The hotly disputed penalty came when Barnes completely mis-timed a header from a corner, but Howard expertly put away the spot-kick by sending Neil Alexander the wrong way as the ball nestled in the right-hand corner.
But Cardiff hit back within four minutes when a mistake by Jay McEveley allowed Parry to get through on the Derby left and his low shot beat the advancing Stephen Bywater and went inside his right-hand post.
A minute later, Chopra burst through on Derby's open left flank and struck a shot that smashed against the bar before re-bounding to safety, but the striker immediately pulled up holding the back of his right leg and played no further part in the game.
Derby's own top marksman was booked just before half-time and Howard will now serve a two-match ban after collecting his tenth yellow card of the season.
But any disappointment was quickly wiped out when Barnes punished hesitant defending by Kevin McNaughton to race clear and restore Derby's lead.
Howard then wrapped it up as the visitors waited in vain for an offside flag that never came.
External Reports
South Wales Echo
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