Barnsley leapfrogged Derby in the League One table with a thumping 4-1 win at Oakwell.
The Tykes made it an impressive seven games without a defeat against Paul Warne’s side, climbing over them into fifth.
An opener was found in the 21st minute, as chaos in the Derby defence gave Devante Cole his ninth goal of the season with a simple close-range strike.
Adam Phillips then scored his third goal in three games, a pass from Jordan Williams finding him outside the box for a right-footed strike to the bottom corner.
The Rams answered back a couple of minutes later with a fabulous finish from David McGoldrick, making it 17 goals this season.
But morale dropped even further for the 5000-strong Derby supporters after fantastic ball movement led to Cole scoring his second goal.
Barnsley secured three points as a fourth goal in added time by Luke Thomas stabilised their play-off position, while Derby now hold the final play-off spot.