Hull squandered a chance to secure promotion to the Barclays Premier League as Barnsley took advantage of the Tigers' end-of-season jitters to boost their survival prospects with a 2-0 win.
It means Steve Bruce's men, now without a goal in three and desperately out of form, hold a one-point advantage over third-placed Watford going into the final round of fixtures, with champions Cardiff heading to the KC Stadium next Saturday.
The Tykes, meanwhile, ended a six-match winless run thanks to early goals in either half from Jacob Mellis and Chris O'Grady, and will guarantee Championship football for next season should they defeat fellow strugglers Huddersfield.
After a dour goalless draw with Bristol City at the KC Stadium last Friday, the Tigers knew their promotion would have been sealed without kicking a ball had Watford lost against either Blackburn or Leicester.
Yet Gianfranco Zola's men recorded back-to-back wins, which meant the 5,900 fans in the away end at Oakwell arrived today with apprehension rather than in celebration.
And that only increased as, in a frantic start, it was the hosts who struck first after four minutes.
Mellis was fed by O'Grady inside the area and, although the angle was against the midfielder, he smashed the ball in via the underside of the crossbar in front of the travelling contingent.
The visitors were rocked and it took them some time to get into their stride, Robbie Brady eventually skewing their first shot on goal just wide.
George Boyd was the next to try his luck as the ball sat up nicely for a half-volley which Tykes goalkeeper Luke Steele easily dealt with.
Hull's frustration was growing and they spilled over just before half-time when Matt Fryatt was denied a free-kick after tangling with David Perkins. The latter squared up to the Tigers striker and the two became involved in a pushing contest in which arms were raised, although referee Chris Foy neglected to use a card of any colour.
The hosts nearly entered the interval two goals ahead when teenager Reuben Noble-Lazarus set off on a driving run from the halfway line which culminated in a weak effort being dragged wide.
Bruce hauled off Boyd for Jay Simpson at half-time, however it was an unlikely source who almost pulled them level with Paul McShane not quite able to make clean contact with his attempt from a free-kick.
Simpson's direct running was stretching the game and Chris Dagnall's deflected cross found the side netting at the other end.
Hull failed to alleviate the pressure, though, and the hosts doubled their advantage five minutes into the second period through O'Grady's sweet strike.
With Dagnall looking for options, O'Grady took the ball off his strike partner's toes and arrowed the ball straight into the bottom corner of the net.
In front of the club's owner Assem Allam, Bruce threw on big-money signing Nick Proschwitz for the ineffectual Fryatt.
But they were left feeding off scraps, Perkins doing well to block Simpson's shot in the six-yard box before Proschwitz somehow failed to connect with a header from a similar range.
The German striker, much maligned among Hull supporters, did manage to get his head on to a Simpson flick-on shortly afterwards but the ball sailed over.
McShane continued to prove a threat from set-pieces and nodded narrowly over from a corner, but Barnsley held on leaving the two sides with contrasting emotions ahead of their respective crunch final fixtures.