Mark Robins secured his first win as Barnsley boss, condemning Derby to their third defeat in a row.
Rob Hulse headed Derby ahead from Lee Croft's cross but Adam Hamill levelled with a stunning long-range strike.
Derby were denied a penalty when Kris Commons appeared to be bundled over and Andy Gray compounded their misery with a goal on the break.
Anderson De Silva rounded the keeper to add a third before Shaun Barker headed in a consolation.
Derby manager Nigel Clough: "We thought it was a foul on Kris Commons (before the second goal).
"Their players stopped and our players stopped. I'm not sure whether it was offside or not, but we've still got to defend it better. We seem to be getting punished at the moment for every little thing.
"There were an awful lot of strange decisions. It's very frustrating when we're battling for everything and we can't get a decision.
"We're not looking for any favours, we're not looking for anything we don't deserve, we're just looking for run-of-the-mill decisions being given correctly.
Barnsley manager Mark Robins:
"I'm pleased for the players because they put a hell of a lot of work in. That's three points from two away games, which is a good return and gives us a platform.
"For us it's a start and it gets us up and running a little bit, but with tough games to come.
"We'll enjoy this, but we've got to turn our attention - once we've looked at some of the injury situations - to the game on Saturday."
90:00+7:30 The game is over, as the referee blows his whistle.
90:00+5:16 Assist by Gary Teale.
90:00+5:16 GOAL - Shaun Barker:Derby 2 - 3 Barnsley Shaun Barker finds the back of the net with a headed goal from close in. Derby 2-3 Barnsley.
90:00+4:59 Corner taken right-footed by Gary Teale,
90:00+2:06 Jacob Butterfield provided the assist for the goal.
90:00+2:06 GOAL - Anderson De Silva:Derby 1 - 3 Barnsley Anderson De Silva grabs a goal from inside the six-yard box low into the middle of the goal. Derby 1-3 Barnsley.
89:54 Stephen Foster gives away a free kick for an unfair challenge on Paul Dickov. Gary Teale takes the free kick.
89:18 Shaun Barker produces a right-footed shot from just outside the box that misses to the right of the goal.
86:48 Shot from just outside the area by Jake Livermore goes over the bar.
84:21 Substitution Anderson De Silva joins the action as a substitute, replacing Emil Hallfredsson.
83:47 Substitution Lee Croft goes off and Stephen Pearson comes on.
77:26 Shot by Hugo Colace from outside the box goes over the net.
75:52 Gary Teale takes a inswinging corner from the left by-line played to the near post, Bobby Hassell manages to make a clearance.
74:33 Corner taken by Gary Teale from the left by-line, clearance made by Darren Moore.
74:10 Corner taken by Kris Commons.
72:46 Paul Connolly gives away a free kick for an unfair challenge on Adam Hammill. David Preece takes the free kick.
71:09 Handball decision goes against Robbie Savage. Direct free kick taken by Stephen Foster.
67:44 Substitution Paul Dickov on for Rob Hulse.
65:04 Darren Moore concedes a free kick for a foul on Rob Hulse. The free kick is swung in left-footed by Kris Commons, Emil Hallfredsson
makes a clearance.
62:34 Direct free kick taken by Robert Kozluk.
62:34 Booking The referee cautions Lee Croft for unsporting behaviour.
62:17 Free kick awarded for a foul by Lee Croft on Robert Kozluk.
61:25 Stephen Foster challenges Rob Hulse unfairly and gives away a free kick. Direct free kick taken by Gary Teale.
61:08 Emil Hallfredsson takes a shot from a long way out which goes wide of the right-hand post.
60:21 Substitution Jonathan Macken joins the action as a substitute, replacing Iain Hume.
59:03 Corner taken left-footed by Kris Commons to the near post, Bobby Hassell manages to make a clearance.
57:47 Foul by Kris Commons on Stephen Foster, free kick awarded. Free kick taken by David Preece.
56:46 The assist for the goal came from Emil Hallfredsson.
56:46 GOAL - Andy Gray:Derby 1 - 2 Barnsley Andy Gray scores a goal from just inside the penalty area to the bottom right corner of the goal. Derby 1-2 Barnsley.
Correction - 55:23 Iain Hume fouled by Miles Addison, the ref awards a free kick. The ball is sent over by Iain Hume, Header by Stephen Foster
from deep inside the penalty area misses to the right of the target.
55:23 Free kick awarded for an unfair challenge on Iain Hume by Miles Addison. Iain Hume takes the direct free kick.
50:08 Outswinging corner taken from the right by-line by Jake Livermore.
48:58 Bobby Hassell concedes a free kick for a foul on Shaun Barker. Kris Commons produces a shot on goal direct from the free kick,
Bobby Hassell gets a block in.
Correction - 47:54 Kris Commons takes a inswinging corner.
47:54 Kris Commons takes a corner.
45:08 Rob Hulse gives away a free kick for an unfair challenge on Stephen Foster. Bobby Hassell takes the free kick.
45:01 The referee gets the second half underway.
45:00+2:16 The match has reached half-time.
44:40 Corner taken right-footed by Adam Hammill, Dean Moxey manages to make a clearance.
44:07 Miles Addison challenges Iain Hume unfairly and gives away a free kick. Free kick crossed right-footed by Iain Hume from right
43:44 Rob Hulse takes a shot. Comfortable save by David Preece.
43:14 Inswinging corner taken right-footed by Gary Teale from the left by-line.
41:47 Corner taken left-footed by Kris Commons, Shaun Barker produces a header from inside the area that goes over the crossbar.
40:46 The referee blows for offside. Indirect free kick taken by Robbie Savage.
37:24 Effort from outside the box by Miles Addison goes wide right of the target.
35:53 Assist by Emil Hallfredsson.
35:53 GOAL - Adam Hammill:Derby 1 - 1 Barnsley Adam Hammill scores from 35 yards to to the top right corner of the goal. Derby 1-1 Barnsley.
34:59 Inswinging corner taken by Iain Hume from the left by-line, Miles Addison manages to make a clearance.
33:49 Close range header by Rob Hulse goes wide of the left-hand post.
31:20 Free kick awarded for an unfair challenge on Andy Gray by Shaun Barker. Iain Hume has a direct shot on goal from the free
29:49 Jake Livermore concedes a free kick for a foul on Iain Hume. Stephen Foster takes the direct free kick.
29:03 Free kick awarded for an unfair challenge on Jake Livermore by Hugo Colace. Free kick taken by Paul Connolly.
28:23 Robert Kozluk concedes a free kick for a foul on Lee Croft. Paul Connolly takes the direct free kick.
27:59 Gary Teale has an effort at goal from outside the penalty area missing to the wide left of the goal.
26:06 The assist for the goal came from Lee Croft.
26:06 GOAL - Rob Hulse:Derby 1 - 0 Barnsley Rob Hulse grabs a headed goal from inside the area. Derby 1-0 Barnsley.
25:40 Corner taken by Gary Teale from the left by-line, clearance made by Robert Kozluk.
24:28 Kris Commons takes the outswinging corner, clearance by Bobby Hassell.
20:49 Unfair challenge on Kris Commons by Darren Moore results in a free kick. Strike on goal comes in from Gary Teale from the
18:56 Adam Hammill decides to take a short corner.
18:27 Long range shot by Dean Moxey goes wide right of the target.
16:18 The referee blows for offside against Andy Gray. Stephen Bywater takes the free kick.
13:33 Corner taken by Kris Commons.
13:14 Rob Hulse takes a shot. Blocked by Stephen Foster.
12:22 Kris Commons delivers the ball from the free kick left-footed from right wing.
12:22 Booking Hugo Colace is shown a yellow card for unsporting behaviour.
12:05 Lee Croft fouled by Hugo Colace, the ref awards a free kick.
9:44 Bobby Hassell gives away a free kick for an unfair challenge on Gary Teale. Robbie Savage takes the direct free kick.
7:22 The referee blows for offside. Robbie Savage takes the direct free kick.
6:22 Free kick awarded for a foul by Jake Livermore on Adam Hammill. Stephen Foster takes the direct free kick.
6:05 Free kick awarded for a foul by Emil Hallfredsson on Lee Croft. Robbie Savage takes the free kick.
5:12 Free kick awarded for an unfair challenge on Jacob Butterfield by Jake Livermore. Stephen Foster takes the direct free kick.
3:22 Free kick awarded for an unfair challenge on Lee Croft by Adam Hammill. Direct free kick taken by Lee Croft.
0:54 Robert Kozluk concedes a free kick for a foul on Robbie Savage. Free kick taken by Robbie Savage.
0:00 The match begins.
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