Derby County fell to a disappointing 4-1 defeat against play-off rivals Barnsley on Saturday afternoon.
David McGoldrick scored his 17th goal of the season but a brace from Devante Cole plus strikes from Adam Phillips and Luke Thomas secured all three points for the hosts.
It was Barnsley that were the first to get in behind and fire a warning sign to the Rams within the opening five minutes through Adam Phillips. The midfielder got down the left and fired a cross-shot across the face of Joe Wildsmith's goal but fortunately there was nobody able to get on the end of it and convert.
Paul Warne's men were struggling to get a foothold in the opening stages and finding the high press of the home side tough to deal with.
Bobby Thomas went close when he headed a Herbie Kane free-kick just wide of Wildsmith's far post before Nicky Cadden's corner caused chaos in the Rams box before being cleared.
It took almost 20 minutes for Derby to first get in behind but when they did it very nearly brought with it a goal. Nathaniel Mendez-Laing did well down the right and pulled it back for Harvey White whose shot was parried by Harry Isted in the Tykes' goal before being hooked away.
Jason Knight then had a venomous half-volley tipped brilliantly over the bar as the Rams finally began to show what they were all about.
The hosts took the lead in controversial fashion soon after through Devante Cole. Adam Phillips nicked the ball into the path of Cole who bundled home and despite massive appeals from the Derby players for offside, the goal was given.
Tom Barkhuizen was inches away from levelling things within a minute of the restart when he headed a David McGoldrick cross onto the crossbar.
Both sides were threatening when going forward but it was Barnsley that were able to double their lead with half-an-hour played. Phillips who provided the assist for the opener turned goal-scorer and bent a brilliant effort past the outstretched Wildsmith.
The Rams responded instantly though through McGoldrick. Conor Hourihane played a brilliant ball through to the striker who made no mistake and dinked a delicate effort past the onrushing Isted to make it 2-1 with just 35 minutes on the clock.
Barnsley were able to restore their two goal advantage right on the stroke of half-time through Cole. The striker initially beat several players in the middle of the park before laying off James Norwood. Norwood's effort was blocked but deflected kindly into the path of Cole who made no mistake and give the Tykes a 3-1 lead at the break.
The Rams came out after the restart eager to find a quick response but chances were becoming really few and far between with the hosts seemingly content to sit back on their two goal cushion.
James Collins and Lewis Dobbin were introduced on the hour as Warne switched the side to a more traditional two up top in an attempt to get back into the contest but the Tykes were standing strong.
Derby were inches away from halving the deficit from a Hourihane free-kick. The Irishman whipped a brilliant ball into the centre of the six-yard box that Collins nor Cashin were able to connect with.
Craig Forsyth blazed over following good play from Tony Springett down the right as time began to run out for the Rams.
With the 90 minutes all but up, Mendez-Laing got away down the right and squared to Dobbin. The winger's first attempt was brilliantly saved by Isted before he poked the rebound wide to sum up what was a day of frustration for Warne's men.
And that frustration was all but compounded when Thomas added a fourth with the last kick of the game. The former Derby player seized upon a defensive error and was able to slot home from the edge of the box in the final seconds to add insult to injury for the Rams.
Barnsley: Isted (GK), Williams, Kitching, Andersen (C), Cadden, Kane (80' Martin), Norwood (71' Tedic), Thomas, Phillips (80' Russell), Cole (71' Thomas), Connell
Substitutes not used: Searle (GK), Cotter, Larkeche
Derby County: Wildsmith (GK), Forsyth (C), Hourihane (77' Springett), Cashin, Barkhuizen (60' Dobbin), McGoldrick, Mendez-Laing, Smith, Sibley (77' Roberts), White (60' Collins), Knight
Substitutes not used: McGee (GK), Thompson, Davies
The Rams return to Pride Park on Tuesday evening when they welcome Cheltenham Town in Sky Bet League One action (7:45pm kick-off).
