Goals from Filip Kiss, Peter Whittingham and a Kevin Kilbane own goal saw Cardiff secure their second away win of the season at Derby.
Midfielder Kiss scored his first goal for the Bluebirds on 20 minutes, finding the net from close range.
Cardiff doubled their lead on 62 minutes when Kilbane conceded an own goal from a Whittingham corner.
And Whittingham secured victory with 17 minutes left as Cardiff moved up to fifth in the Championship.
Derby's unbeaten run of four home games was ended as Cardiff produced their first away win since their opening day victory at West Ham in August.
Kilbane and 15-year-old striker Mason Bennett were the two changes to Derby's side while Kiss and Kenny Miller returned for Cardiff.
Kiss had already forced keeper Frank Fielding into making a fine save before the Slovakian international gave Cardiff the lead on 20 minutes.
Ben Turner teased a ball across the Derby backline to Kiss, who dug out a dipping drive to beat Fielding at his near post.
There was a notable change in Cardiff's line-up for the second half with substitute keeper Tom Heaton replacing David Marshall, who felt unwell at the interval.
And it was the visitors who had the first chances of the second period with Whittingham firing past the post and Aron Gunnarsson trying his luck from distance.
Cardiff were in control and Craig Conway slammed a snapshot across the goalmouth and wide before Whittingham saw his powerful shot blocked by Jeff Hendrick.
Derby rarely threatened with Jason Shackell wasting a good chance when he headed over the crossbar from a Ben Davies corner.
Cardiff doubled their advantage on 62 minutes with Kilbane heading into the roof of his own net following Whittingham's corner.
Malky Mackay's side wrapped up their victory on 73 minutes when Kiss supplied Whittingham just inside the area for the former Aston Villa player to fire home.
Derby pushed for a consolation during the final 10 minutes but Hendrick's speculative drive was blocked by Gunnarsson and substitute Tomasz Cywka was denied by Heaton.