County recorded a seventh straight win against Neil Warnock's disorientated side.
In a meeting of two of the division's also rans for the season, Craig Bryson's 31st-minute wonder goal and Steven Davies' second-half effort sealed the success, but only after Leeds had lost experienced midfielder Michael Brown to a red card following a studs-up tackle on Theo Robinson.
Brown's dismissal was United's third in as many games and their ninth of an up-and-down season. Fancied for promotion in August they are now woefully out of form, are headed for a bottom-half finish and have lost 10 of their 21 games at home.
Warnock has yet to win a game in front of his own fans since being appointed in February either, and his assessment that the squad he inherited from Simon Grayson needs major surgery looks a sound one.
Derby, though, can head towards the summer with optimism after an impressive display.
Even before Brown's hot-headed moment they had impressed and enjoyed all the possession and chances. After Bryson's goal the result was never in doubt and they saw out a game they deserved to win from the off.
As early as the first minute Jake Buxton had a header saved by Andy Lonergan and Nathan Tyson headed the rebound over an open goal, while only a fine cover tackle from Tom Lees denied Tyson after Robinson's run and cross.
It was all Derby and Paul Green nodded over following a round of head tennis, before Brown was dismissed by Oliver Langford in the 26th minute for a reckless-looking raised foot into the midriff of a standing Robinson.
The veteran looked perplexed at the decision but replays suggested the official was correct to make it and, six minutes later, County were ahead when Bryson made the most of a pocket of space outside of the D and curled a delightful 25-yard effort high of Lonergan.
They thought they could have had a chance of a second not long after, but Langford rejected his linesman's claim of a handball in the box and, following that, Leeds finished the half stronger with Ross McCormack and Luciano Becchio both going close.
The Whites had the first genuine chance of the second half too, with Frank Fielding doing well to punch away Robert Snodgrass' fizzing free-kick, while the former England squad man also got down well to deny Ramon Nunez.
Brown's absence had left Leeds woefully short in midfield, though, and after Derby walked through with 66 minutes gone, they made it two.
They got into the area with some ease, Davies had a shot that was charged down, but was on hand to lash home when the ball fell back into his path.
Any shape Leeds may have had quickly disappeared with their players reverting to a flurry of swings and kicks as Derby's players skipped around them - much the same as what happened in their bad-tempered defeat at Reading on Friday.
They could have pulled a goal back when Danny Webber skewed wide when clean through, but were also fortunate not to concede in the dying seconds when Lonergan denied Davies what would have been a crowning third.