Florian Jozefzoon scored against Hull for the third time in the last two games
Florian Jozefzoon's late strike piled more pressure on Hull boss Nigel Adkins as Derby inflicted a fourth successive home defeat on the Tigers.
Martyn Waghorn converted from the spot after David Nugent was brought down by Jordy de Wijs to give Frank Lampard's side a deserved first-half lead.
Hull equalised against the run of play as Todd Kane converted after an excellent through ball from Evandro.
But Jozefzoon's deflected shot at the back post beat David Marshall following a low cross from Mason Bennett.
It was the second time in four days that Derby had won at the KCOM Stadium - they were 4-0 victors in the second round of the Carabao Cup at Hull on Tuesday, when Jozefzoon scored twice.
Hull have scored just twice at home in all competitions this season, losing four of their last six games and are above the relegation zone by goal difference only.
Derby, who rose to fourth after a fourth successive win in all competitions, could have had the game settled well before half-time.
Waghorn had an early penalty appeal turned down, while with six minutes left of the half the impressive Mason Mount forced David Marshall into great save before Nugent headed the resulting corner against the bar.
After Kane's equaliser, Hull could have gone ahead as Derby failed to clear their lines and Evandro put an effort narrowly wide of Scott Carson's goal before the former England stopper saved well from Markus Henriksen with 20 minutes left.
Hull City boss Nigel Adkins said:
"I thought we were very good today. I talked on Tuesday night about what a good side they were. Today I thought technically we were spot-on.
"The penalty looked a very clumsy challenge. David Nugent being an experienced forward has obviously ended up on the floor and the referee has chosen to give a penalty.
"The passion was there for all to see, the quality was there for all to see and the team spirit was there."
Derby County manager Frank Lampard:
"It was a tough game, the second half was very tough. That's the Championship.
"Full credit to Hull. They will feel they deserved a draw.
"We showed great character. We were under pressure at times, particularly in the second half."
