Ricardo Vaz Te struck a hat-trick as Barnsley ended a run of three consecutive defeats by completing the double over Yorkshire rivals Leeds.
The Portuguese fired past Andy Lonergan to open the scoring after referee Neil Swarbrick had played a good advantage.
His ninth and 10th of the season, separated by Craig Davies' long-range effort, followed from Matty Done's corner and Bobby Hassell's pass.
Luciano Becchio headed in late on, but it was little consolation.
The Tykes are now just two points behind Leeds - who themselves are two points away from the play-off zone.
The visitors, for whom chairman Ken Bates has insisted that promotion is a must this season, have now gone four games without a win.
Vaz Te began the afternoon on the bench, but took his chance superbly after being thrust into the action on 15 minutes following an injury to Jacob Butterfield.
Leeds could have taken the lead as Andy Keogh went close with the scoreline still blank, but his team were comprehensively beaten and the match finished with home fans questioning whether visiting boss Simon Grayson would keep his job.
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