Ricardo Vaz Te made an unexpectedly early appearance from the bench to fire a brilliant hat-trick and inspire Barnsley to a 4-1 win and first league double over Leeds in 22 years, turning up the pressure on United manager Simon Grayson in the process.
Vaz Te, a goalscorer in the Tykes' 2-1 win at Elland Road last month, was an unwelcome sight on the touchline for the home fans in the 15th minute, with his introduction a direct result of an injury to captain Jacob Butterfield - the club's outstanding player this season.
But the well-travelled 25-year-old, who has finally found a home at Oakwell under the careful guidance of Keith Hill, more than cushioned the blow of Butterfield's absence with a well-taken treble that took his tally to the season for 10.
His goals came in the 16th, 50th and 72nd minutes, with Craig Davies adding a wonderful third on the hour. Leeds barely looked like scoring one until Luciano Becchio's late consolation, and Grayson could be forgiven for wondering if he will be in charge of the side against Burnley on Monday.
He has been told by owner Ken Bates that promotion is a must this season, and this, the worst of a four-game winless run, is sure to make an impact at the outspoken veteran's Monte Carlo base.
Leeds actually started as though that would not be the case, with Andy Keogh going close. That chance aside, though, the opening 15 minutes were largely lifeless, before the game ignited inside the space of 60 seconds.
First, Leeds' Ramon Nunez fizzed a shot wide from 25 yards, before Butterfield - widely expected to leave Barnsley in January as he approaches the end of his contract - limped off following an earlier challenge from Darren O'Dea.
But Barnsley were not hamstrung by the loss of their star man and, within moments, the man who replaced him, Vaz Te, slotted under Andy Lonergan after Patrick Kisnorbo had failed to clear following a Davies run.
One could quickly have become two had Matty Done shown a better far-post touch when Vaz Te played him in, before Nunez again went close, Luke Steele this time pushing a long-range hit wide.
The game was open now and Barnsley had a reasonable penalty appeal turned down when Aidy White appeared to handle in the box, while O'Dea was unlucky to see a well-executed overhead slip past the target.
Davies then spurned a far more presentable chance as he powered well over from 10 yards after Done's lay-off, but the pace of both Davies and Vaz Te was causing Leeds all sorts of problems, with O'Dea, Michael Brown and Mika Varynen all in constant dialogue with the referee as they resorted to late tackles in a bid to stem the flow.
Poor decision-making was also costing United, with Done nearly curling one in four minutes after the restart following a hashed clearance from Kisnorbo.
The Australian then hesitated in the box and needlessly conceded a corner, from which Vaz Te would add his second. The ball found the Portuguese unmarked at the back post and, even though he was eventually closed down by Danny Pugh, he had already picked his spot beyond Lonergan.
Grayson responded with a double substitution, introducing Becchio and Adam Clayton, but there was little his forward players could do on the hour as Davies whipped in a delightful third goal, giving Lonergan no chance from the corner of the box with an effort which was pinned to the top corner.
Aware of the mounting pressure on Grayson, the home fans taunted him with chants of "you're getting sacked in the morning' - with the Leeds fans option to direct their ire at their absent chairman.
The day belonged to Vaz Te, though, and he wrapped up a well-deserved treble with 18 minutes left, turning O'Dea one way and then the other before finishing under Lonergan.
Becchio nodded in an injury-time consolation for Leeds from a Nunez free-kick.