Craig Noone's sending-off proved costly for Championship leaders Cardiff as Derby hit back to claim a deserved 1-1 draw that maintained their fine record at Pride Park.
After falling behind to Heidar Helguson's close-range header in the 11th minute, the Rams, who have lost just once at home this term, enjoyed much the better of proceedings.
Yet it was only after Noone had seen red for two yellow cards in the space of three second-half minutes that Derby found a way through, with Theo Robinson converting a square pass from Craig Bryson.
Cardiff boast a perfect record at home this term, but points on the road have proven harder to come by, with Saturday's triumph at Barnsley only their third away win in nine attempts.
Malky Mackay's men defended resolutely on this occasion, but could have few complaints at being denied a fifth successive league victory over Derby.
Craig Bellamy and Joe Ralls replaced Joe Mason and the suspended Simon Lappin in a Cardiff line-up still missing several players through injury, while County were unchanged after young midfielder Will Hughes shook off an ankle knock.
Both sides had chances prior to the visitors' early opener.
Bellamy should have done better when firing high over the bar from 25 yards, while Derby skipper Richard Keogh leapt highest to meet a right-wing corner, only for Noone to scramble the ball off the line.
Cardiff were soon in front courtesy of Helguson, who was on hand to nod home a rebound after Mark Hudson's looping header had been tipped on to the crossbar by Adam Legzdins.
Michael Jacobs curled an effort narrowly wide and Hudson produced a fine aerial clearance to deny Robinson as Derby responded well.
After Kim Bo-kyung and Bryson had seen chances go begging at either end, the Rams were then forced into a change in the 28th minute as Gareth O'Connor replaced a limping Gareth Roberts.
Nigel Clough's men finished the first half stronger and David Marshall pulled off a fine low save to deny Paul Coutts before Jake Buxton sent a header on to the roof of the net.
Cardiff remained on the back foot after the interval, but could have extended their lead when Bellamy broke clear on the counter. However, the veteran forward once again failed to keep his shot down.
Strong appeals for a Derby penalty were waved away after Noone appeared to block Bryson's goalbound shot with his arm. Yet within seconds, the Cardiff winger was handed a second booking in quick succession following a late challenge on Hughes.
The hosts swiftly capitalised as Bryson surged into the area before squaring to leave Robinson with the simplest of tap-ins.
Helguson almost restored his team's lead when he beat Legzdins to a left-wing cross, yet the momentum remained with Derby and full-back John Brayford twice went close before another shout for handball in the Cardiff area, this time by Peter Whittingham, fell on deaf ears.
Ultimately, the Welsh side were able to hold on, although Paul Connolly was forced to head off the line during six minutes of injury-time.