Derby punished Michael Brown's red card to record a seventh successive win against Leeds thanks to goals from Craig Bryson and Steven Davies.
Minutes after Brown's first-half dismissal for a stomach-high challenge on Theo Robinson, Bryson curled a 25-yard effort past keeper Andy Lonergan.
Derby continued to exploit their one-man advantage and Davies had time to slot home a rebound to double the lead.
The result moved the Rams to within five points of the play-off places.
Brown's sending off was Leeds's third in as many games, and ninth in a disappointing season which sees them locked in mid-table.
Derby should have gone ahead in the first minute, but Nathan Tyson headed the rebound from a Jake Buxton chance over an open goal.
Leeds enjoyed their best period of the match either side of the interval as chances were spurned by Ross McCormack, Luciano Becchio and Robert Snodgrass before Davies sealed the three points.
The result extends manager Neil Warnock's wait for a first Elland Road win to five games since he took control of the team in February.
Leeds manager Neil Warnock: "The end of the season can't come quickly enough.
"I said to [Derby manager[ Nigel Clough at the end, 'Enjoy this, Nigel, because you'll never see another Leeds United team or a Neil Warnock team like this'.
"We had a lot of players playing today that know they won't be here next season. We've not got enough Leeds United-type players.
"We don't revel in the atmosphere and that's what we will do next year. We will revel in it."
Derby manager Nigel Clough: "I want to try to keep these lads together.
"Two or three of them are out of contract. I want to try to keep them and the spirit together and take the confidence into next August.
"If we had another four games, maybe [the play-offs would be an option], but we might just run out of time."