First-half headers from captain Richard Keogh and on-loan striker Chris Martin saw Derby end their Leicester hoodoo with a 2-1 victory at Pride Park.
After five successive npower Championship defeats against the Foxes, Nigel Clough's side broke the sequence with a vital three points to move them clear of the relegation zone.
Substitute Jeff Schlupp pulled a goal back for the visitors just after the hour mark but Leicester could not rescue anything from the game as their winless league run reached five matches.
Frank Fielding returned in goal for Derby in one of four changes made by Rams boss Clough.
Fielding replaced Adam Legzdins to make his first appearance since losing his place through injury at the start of October.
With Gareth Roberts out with a knock sustained in training this week, on-loan Watford midfielder Craig Forsyth filled in at left-back.
Leading scorer Jamie Ward, midfielder Craig Bryson and right-back Kieron Freeman all returned from injury as Ben Davies and Valentin Gjokaj dropped to the bench.
Leicester manager Nigel Pearson made one change to his side, recalling fit-again left-back Paul Konchesky in place of striker Schlupp.
Andy King headed over the crossbar as the Foxes attacked early on but it was Derby who took the lead after 16 minutes.
Leicester captain Wes Morgan conceded a free-kick wide on the left and Keogh glanced home Ward's delivery from six yards out.
A mistake by Jeff Hendrick midway through the first half almost led to an equalising goal.
The midfielder lost possession to opposite number Richie Wellens on the edge of his own box but Lloyd Dyer scuffed his volley after being picked out at the far post by David Nugent, who was denied by Fielding shortly afterwards when he let fly from long range.
Derby felt they should have had a penalty in the 40th minute when Wellens tripped Freeman just inside the area down the right-hand side.
The Rams finished the first half on top and almost extended their lead when Ward escaped down the left before setting up Martin, but the man on loan from Norwich saw his shot saved by Kasper Schmeichel.
Martin would not have to wait long for a goal, however, as he headed home Forsyth's left-wing cross a minute before the half-time whistle.
Schlupp, who in Konchesky's absence had been filling in as a makeshift left-back, was introduced at the start of the second half with Wellens making way.
And the 20-year-old, who recently spent a month on trial at Manchester United, got Leicester back into the game after 62 minutes with an arrowing left-footed strike across Fielding after being teed up by Nugent's lay-off.
The German-born Ghana international continued to make a nuisance of himself and almost returned the favour for Nugent in the 70th minute, but this time Fielding made the save.
At the other end, substitute Davies worried Schmeichel with a 25-yard shot but his effort was always rising and narrowly cleared the crossbar. Martin's deflected strike then looped kindly into the hands of the Dane.
Leicester pushed for an equaliser but never really tested Fielding as Derby held on for a first Championship victory in nine outings to climb into the top half of the table.
Leicester had been pushed down to sixth with Nottingham Forest's win at Hull earlier in the day and Pearson's team remain in the final play-off spot.