Daniel Bogdanovic's early quick-fire brace ended Barnsley's three-match losing streak in style as they secured a shock 2-0 victory to dent Cardiff's promotion ambitions.
The Libya-born Maltese international capitalised on some slack City defending to register his sixth and seventh Coca-Cola Championship goals of the season with just 12 minutes on the clock, boosting the Yorkshire club's own play-off hopes.
The goals certainly came against run of the play during a first half in which Cardiff repeatedly threatened but remained largely toothless in attack.
Both sides had opportunities to add to the scoreline after the break but it was the hosts who again controlled the majority of proceedings without taking their chances, with Peter Whittingham and Kevin McNaughton both hitting the woodwork while Tykes keeper Luke Steele pulled off some marvellous saves.
It was the first time since Boxing Day that Cardiff have failed to find the net and the defeat leaves manager Dave Jones still waiting for his 100th win in charge of the Welsh club.
Peter Enckelman came in for his first league start in over a year with Bluebirds number one David Marshall confined to a place on the bench due to a medial ligament injury.
Barnsley made four changes from the side that lost 2-1 at Scunthorpe in midweek - Bogdanovic, Jonathan Macken, Bobby Hassell and Luke Potter coming in.
As expected, it was Cardiff who started very much on the front foot with Michael Chopra wasting a great early opportunity.
And he was left to rue the miss in a big way as the visitors took a stranglehold on the encounter with virtually their first two attacks of the game.
Centre-back Gabor Gyepes was found wanting with nine minutes on the clock and he presented Bogdanovic with a clear run on goal before firing past the helpless Enckelman.
And it was soon 2-0 as Bogdanovic capitalised on an even bigger space in the home defence - with Gypes arguably at fault once again - to leave the home crowd stunned into silence.
Whittingham blazed over when presented with a chance to halve the deficit midway through the half, and Jones would have hoped Cardiff's lack of invention in the final third would have been enhanced by Ross McCormack's 35th-minute introduction from the bench.
Yet despite Cardiff's attacking intent Barnsley remained untroubled, with Hugo Colace blowing a wonderful headed chance to add a third in first-half stoppage time.
The home side must have received a rocket at the interval and started the second half with intent, Whittingham clipping a post with his free-kick.
But Tykes midfielder Adam Hammill was determined to wrap up the contest and he forced two fine reaction saves from Enckelman to keep City in it.
The next goal was certain to prove crucial and opposite number Steele was on hand to push Chopra's shot and Gyepes' header to safety.
Cardiff were applying a host of pressure and McNaughton saw his strike smack the underside of crossbar and bounce away to safety.
Steele was then again on hand to deny Chopra and, although substitute Andy Gray headed off target at the other end, Barnsley enjoyed a comfortable close to the encounter to secure a league double over the Bluebirds.
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