Barnsley midfielder Hugo Colace snatched a second-half winner in a 1-0 victory against Leicester - the Tykes' first Coca-Cola Championship success of the year.
The Argentinian pounced to steer home a rebound after Ryan Shotton's towering header from Iain Hume's 77th-minute corner had been brilliantly saved by visiting goalkeeper Chris Weale.
Barnsley's recent steady climb towards the top half of the table had faltered in recent weeks after successive league defeats to Coventry and Sheffield Wednesday.
Mark Robins' side also crashed out of the FA Cup at Scunthorpe during a run of three successive defeats, but deserved their fifth home win of the season by shading their opponents in the second half after a dismal first period.
Nigel Pearson's Foxes began the game only one point adrift of the play-offs, but they are left chasing their first win of 2010 and followed up their disappointing FA Cup exit at Cardiff with another mediocre showing in front of a crowd of 12,065 at Oakwell.
Barnsley defender Rob Kozluk, midfielder Anderson De Silva and striker Hume all returned to the Tykes' starting line-up, while Leicester made just one change with David McGivern making way for Chris Powell.
Neither side had had a shot on goal when Barnsley midfielder Nathan Doyle burst out of the tedium in the 28th minute to intercept the ball in midfield before bearing down on the visitor's penalty area.
Doyle threaded a weighted pass through for Hume, but Leicester centre-half Wayne Brown rescued his side with a brilliant last-ditch cover tackle to ensure Weale did not have to make the game's first save.
Leicester's Dany N'Guessan blazed his side's first shot at goal high and wide, but home goalkeeper Luke Steele denied Martyn Waghorn in the 38th minute with a fine sprawling save and Tykes skipper Stephen Foster blocked N'Guessan's follow-up to keep the first half goalless.
N'Guessan then headed just wide when unmarked from Paul Gallagher's cross just before the interval.
Hammill lit up the second half with a searing 30-yard drive that Weale turned away at full stretch in the 54th minute.
Desperate Leicester defending kept the scores level from the subsequent corner when Shotton and Foster both saw their respective headers cleared off the goalline by Matt Oakley.
Hammill's low shot, after he had wriggled into the area, was then saved by Weale as the game sparked into life and Hume toe-poked wide from 10 yards.
Leicester sent on strike pair Steve Howard and Matt Fryatt in the 66th minute, but Barnsley still pressed and Shotton's cross-shot arced agonisingly wide soon after.
Andy King replaced Foxes winger N'Guessan in the 74th minute and Jon Macken made way for Andy Gray moments before Barnsley broke the deadlock.
Shotton powered Hume's corner towards the bottom corner and although Weale kept the ball out one-handed, Colace pounced to side-foot home the rebound in the 77th minute.
Weale saved in fine style again from Anderson thundering half-volley and although Leicester forced successive late corners the home defence held firm.
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