Barnsley earned their first Championship win since returning to the second tier, with Conor Hourihane creating both goals against Derby.
The Tykes took the lead even before getting a shot on target, with captain Hourihane’s effort from 25 yards coming off the post before rebounding off Rams goalkeeper Scott Carson into the net.
Alfie Mawson met a Hourihane free-kick to head home a second after the break.
Ryan Kent also hit the post for Barnsley as Derby remain winless.
The defeat is the Rams’ first under former Leicester City boss Nigel Pearson, who took charge in the summer, following the goalless draw with Brighton in the league and EFL Cup victory over Grimsby.
Barnsley started strongly with Kent particularly threatening down the right-hand side, where he linked up with Aidy White to create the chance for man of the match Hourihane and the game’s opening goal.
Derby’s troubled started was compounded by injuries, with Republic of Ireland international Jeff Hendrick forced off moments after the goal, to be replaced by Will Hughes. Former England striker Darren Bent, who also took a knock in the opening 10 minutes, was also eventually replaced by Chris Martin at half time.
Mawson made it 2-0 and Kent went close before substitute Johnny Russell got the Rams’ first shot on target after 65 minutes, with Tykes goalkeeper Adam Davies going on to make a series of fine saves from Tom Ince, Craig Forsyth and Russell.
Barnsley head coach Paul Heckingbottom:
“Everyone can see the energy and the hard work that the players put in. We started both halves really well, got the goals at key times and defended stoutly throughout. It was a deserved win and we’ll take a lot of belief and confidence from it.
“We know we might play like that in some games and get beaten but hopefully with the quality we’ve got we can cause teams problems. I thought in both boxes we were much better than last week. We took our chances and were ruthless with how we defended our own box.
“Last season we had a really good winning mentality. That’s what we needed to show in this game and we did. It was a good example of what it takes to win a game of football in this division. I hope the fans enjoyed it and appreciated just how much effort the boys put in.”
Derby County boss Nigel Pearson:
“There are a few psychological issues to address in the sense that we’ve got a few players who are out of form and they’ve got to try and find a way back into form.
“I’ve got to manage the players through that process. It’s never easy and people have their own opinions on things but what we’ll do is get back to work and try and rectify what has been a difficult and disappointing afternoon.
“We don’t like it when we’ve got a good following and we let our fans down but more importantly we don’t want to let ourselves down and we’ve done that here. It’s my team and it’s my job to rectify that and I will do that.
“People have different ideas of formations and style of play but if you look at the side we had out there today, I could easily have played two or three different formations. It’s difficult because of changes for the new season.”
Match ends, Barnsley 2, Derby County 0.
Second Half ends, Barnsley 2, Derby County 0.
Delay over. They are ready to continue.
Delay in match Josh Scowen (Barnsley) because of an injury.
Substitution, Barnsley. Elliot Lee replaces Adam Hammill.
Foul by Johnny Russell (Derby County).
Alfie Mawson (Barnsley) wins a free kick in the defensive half.