Middlesbrough were punished for failing to take their chances as Bobby Clark fired Derby to a 1-0 win at Pride Park.
The visitors dominated the game but lacked a ruthless edge inside the Rams box and Clark took advantage with a second-half winner.
The midfielder showed the composure with his finish that Boro craved to earn Derby a first home win since November 4 and condemn the visitors to a third defeat in four matches.
Boro had failed to score in their previous three games and missed two great chances in the space of a minute.
First, Hayden Hackney was played in by Delano Burgzorg in the eighth minute and tried to dink the ball over Jacob Widell Zetterstrom but couldn't get it over the goalkeeper.
Tommy Conway then completely missed his kick when through on goal and, as the visitors dominated, Morgan Whittaker had a shot deflected over.
Derby were struggling to get any spells of possession and when Ebou Adams gave the ball away, Hackney blazed over from the edge of the box.
The worry for Boro was they had failed to make their superiority count and another chance was spurned in the 28th minute when Conway's volley from an unmarked position was pushed away by Zetterstrom.
The Derby keeper was relieved to see a low drive from Burgzorg whistle just past his right post in the 42nd minute and Boro's Sol Brynn was called into action for the first time to turn behind a Joe Ward free-kick at the end of a half which had belonged to the men in red.
Boro started the second on the front foot with Burgzorg bringing another save from Zetterstrom but Derby had their best chance in the 55th minute.
Callum Elder played Patrick Agyemang through on the right but Brynn came out and did enough to deny the American forward.
Boro wasted another chance with Burgzorg shooting over in the 64th minute and they were made to pay when Derby went ahead in the 70th minute.
Elder found Lars-Jorgen Salvesen just inside the box and Clark took it off the striker before firing low past Brynn.
Boro's defending was questionable but they only had themselves to blame after wasting so many opportunities.
Despite seven minutes of added time, they could not manage a response with Alex Gilbert's wayward overhead kick summing up another frustrating afternoon for the promotion chasers.
Derby's John Eustace:
"Middlesbrough started really well, we weren't expecting them to start like they did with their shape and their build-up so it took the lads and myself by surprise a tiny bit.
"But I thought we adapted really well, we did ride our luck a little bit but to come away with a 1-0 victory, I'm delighted.
"Second half, I felt very much more in control of the game, we adapted a couple of things in our shape and structure.
"It doesn't matter how well you start or the opposition start, you have to stay in the game. There have been moments throughout the season where we have been doing very well at times but then conceded a really sloppy goal."
Middlesbrough's Kim Hellberg:
"For the moment, football is very, very cruel to us and we have to sort it out and turn it around.
"I am very happy with how we performed, the first 60 minutes we were very good and created a lot of opportunities and we should have killed that game off.
"But we didn't and then you know that in this league you cannot keep a very good team from not creating anything at home.
"If you look at how we created over the last eight games, I think we have the most shots in the league so we are creating a lot of chances, a lot of good chances and are having a lot of balls into the box."
