Derby took another step on the road to a great escape in the Championship but it leaves Hull sixth bottom, although with a 12-point advantage over the bottom three.
Wales international Tom Lawrence scored and laid on another for Festy Ebosele after Craig Forsyth gave Derby a first-half lead they never looked like relinquishing. The defender headed past Matt Ingram on his 250th appearance for Derby who, despite still being in administration, are now only four points behind fourth-from-bottom Reading, who have played two games fewer.
Hull started well enough with Keane Lewis-Potter forcing Ryan Allsop into a flying save but the night went rapidly downhill for the Tigers after Forsyth put Derby ahead.
They did at least respond in the second half and pulled a goal back when Forsyth deflected in a Lewis Potter cross but it is now back-to-back defeats for Hull.
Lewis-Potter found space on the edge of the area to fire in a shot which Allsop did well to turn behind. Derby were moving the ball quickly and getting crosses into the box although Hull almost hit them on the break in the 15th minute when Marcus Forss whipped the ball in and Lewis-Potter headed wide.
But Hull were stunned four minutes later when Jason Knight crossed from the right and Forsyth climbed above Lewie Coyle to power a header into the top right corner.
Derby threatened whenever they went forward and it was no surprise when they increased their lead in the 38th minute. Ebosele used his strength to power his way to the byline and when Ingram could only push the ball away, Lawrence pounced to score from six yards. Lawrence then drove forward and played in Ebosele who fired in a low drive which flew past Ingram’s right hand and inside the far post.
Hull at least showed some fight and reduced the deficit in the 65th minute when Lewis-Potter went past Ebosele on the left and his cross went in off Forsyth.
Derby County: Allsop, Byrne, Davies, Buchanan, Forsyth, Bielik (Thompson 81), Bird, Ebosele (Sibley 70), Knight, Lawrence, Plange (Ebiowei 90). Unused substitutes: Roos, Bardwell, Stretton, Cashin.
Hull City: Ingram, Jones, McLoughlin, Greaves, Coyle (Eaves 75), Walsh (Sayyadmanesh 65), Docherty (Huddlestone 89), Fleming, Honeyman, Forss, Lewis-Potter. Unused substitutes: Smallwood, Longman, Bernard, Cartwright.
Referee: G Eltringham (Tyne & Wear).