Reading tore up the form book and Derby's hopes of a fifth consecutive win when they claimed a shock 4-2 victory at Pride Park.
The Championship strugglers were always in control after Liam Moore and Sone Aluko scored in the opening 13 minutes and Roy Beerens made it three before Johnny Russell pulled one back. Modou Barrow scored a fourth and although Chris Martin replied in the 90th minute, Reading had done enough.
Derby suffered an early double blow when skipper Richard Keogh went off in the eighth minute holding the top of his right leg and then Reading went ahead a minute later. Alex Pearce had just replaced Keogh when a free-kick from the left was flicked on by Paul McShane and Moore climbed to head in at the back post.
It was deserved because Reading had dominated possession and they scored again in the 13th minute when John Swift played in Aluko who jinked past two challenges before firing past Scott Carson from 12 yards.
Derby manager Gary Rowett waved his arms in frustration at the room Reading were given in the build-up to the goal and the game was certainly not going to plan for his team.
Reading were moving the ball with purpose and controlling the tempo while Derby's first half performance was summed up by a free-kick from just outside the area that went harmlessly wide.
Rowett's words at half-time clearly got through because Derby came out fired up and Craig Forsyth's cross just evaded two white shirts before David Nugent headed just wide.
It was the first real pressure Reading had been under and Tom Lawrence tested Vito Mannone with a swerving 20-yard drive before a dreadful error gifted the visitors a third in the 54th minute. Curtis Davies played the ball inside from the left but only found Beerens who went round Carson before side-footing into the empty net.
It could have been four in the 60th minute when Reading had two against one on the break with Beerens setting up Barrow but he shot at Carson and the same combination caught Derby again two minutes later with Barrow this time firing wide.
Reading had played a dangerous game at the back with short passes in and around their area and it bit them in the 71st minute when Mannone gave the ball to Bradley Johnson and he set up Russell to score from eight yards.
But the three-goal cushion was restored four minutes later when Reading broke again and this time Barrow made no mistake when David Edwards' cross found him unmarked. Martin converted Andre Wisdom's cross but it was too little, too late for Derby.
The managers
Gary Rowett: "After 10 minutes, I was looking to see where the pumpkins were, I thought I had missed something and it was Halloween this evening. It was a very poor start and you could see after a couple of minutes that we were really slow to react to things and very low in energy. We didn't get close enough all over the pitch and it almost took us to go 2-0 down to start to run around.
"I felt if we got the next goal we were still in the game and we looked as though we were getting close when we make an uncharacteristic error at the other end. We looked like there was no real spark, whether that's because people are saying nice things about us and we are in the play-off positions, I don't know but ultimately we didn't turn up and perform early in the game and didn't defend well enough as a team."
Jaap Stam: "Derby was a team in form, they were in a good flow and getting results. We studied them in the last couple of games and what they are doing, how they get their goals, how they defend and where can we hurt them and I thought the boys have done very well.
"They stayed calm, kept possession and we scored early goals which made them go forward even more which opened up spaces - and we should have scored at least a fifth goal. Everybody is looking at the table and if you are not winning, think you aren't playing well but that wasn't the case with us. A lot of games we played well but our mistakes cost us."