TOWN paid heavily for a disgraceful first half showing at Oakwell to leave prospects for the season hanging in the balance.
It was Macclesfield all over again as shambolic Town were completely outplayed in all departments to be three down at the break.
And, despite a rip-roaring fightback against 10 men in the second half - when substitutes Lee Fowler and Andy Booth made a big impact - Town's misery was compounded by a late moment of madness from keeper Paul Rachubka which presented Barnsley with a match-clinching penalty to complete Michael Chopra's hat trick.
The decision against Rachubka may have been harsh, but referee Trevor Kettle was so inconsistent that the keeper's lunge in retaliation to Chopra's flailing boot was highly charged with risk.
The successful spot-kick effectively ended Town's chances of pulling off a remarkable recovery in an eventful derby and left them to reflect on what might have been if only they had competed in the first 45 minutes.
On a ground where seven years ago manager Peter Jackson saw Town concede a club record six first-half goals, he must have been worried about a similar mauling as Barnsley were allowed to dominate every aspect before the boos of 2,500 travelling fans preceded a much-needed half-time reshuffle.
Chopra had netted on nine and 23 minutes before Michael Boulding - rejected by Town after several Reserve outings a few years ago - waltzed through to fire a third after 38 minutes of a grossly unpalatable half for the visitors, who were in such a mess they fashioned not a single decent pass to debutant loan striker Luke Beckett.
Jackson sent on Steve Yates for injured centre-back Nathan Clarke at the start of the second half and, crucially, introduced Lee Fowler to midfield to give the side much more shape, direction and bite.
It was the sending-off of Barnsley keeper Ross Turnbull on 50 minutes which helped open up the game - he tripped Beckett for a penalty after a brilliant through ball from Chris Brandon - and substitute keeper Nick Colgan could feel aggrieved to be penalised for moving off his line when saving Pawel Abbott's first spot-kick before the big striker blasted in the re-take for his 18th goal of the season.
Town, with their bank of fans responding magnificently to the revival, were suddenly back in business and, when Booth went on for the injured Andy Holdsworth with 35 minutes left, they were totally transformed.
All the 50-50s which were lost in the first half were now being won, Fowler provided width and passing range and, with Booth's aerial power seeming to scare Paul Hart's side, Town produced some fluent attacking moves.
Only a brilliant reaction save by Colgan prevented Sheffield United's Beckett netting from a Tony Carss and Booth build-up on the hour, and Hart was desperately trying to get on big substitute defender Matt Carbon when Booth reduced the deficit to just one with 69 minutes on the clock.
Town were all over the Reds at that stage - Boulding and Jamie Burns stemming the flow only with shots on the breakaway - and Jon Worthington was twice close with shots before Booth and Beckett had efforts saved on the line by the agile Colgan.
When Carss, playing freely at left-back, and Worthington combined to set up Abbott for a shot against the bar and Booth drilled another effort inches past the angle, an equaliser seemed inevitable and the Barnsley fans who had earlier chanted `we want seven' in recognition of that 1998 result were strangely silent.
They rediscovered their voice only when Rachubka conceded the penalty from which Town let in four at League level for the first time since Macclesfield last season, a result which proved a turning point in the campaign.
For this defeat to have similar effects, Town have to find some defensive mettle throughout the side and not become such a soft touch when the wheels fall off.
Two wins in 15 is far from encouraging with a nine-point gap to the play-offs and 10 to the drop zone, but it's the one clean sheet in the last 20 League games which really highlights the current problem facing Town and their defiant manager.
Man of the Match: Lee Fowler
Gave much-needed direction and bite to a Town side who had been completely outplayed in the first half. Just pipped Andy Booth to the award and would have got seven out of 10
How they rated:
Paul Rachubka Poor display by his high standards and he will regret the retaliatory lunge at Chopra which handed Barnsley safety Rating: 3/10
Nat Brown Supplied some decent crosses from right-wing raids in the second half when linking well. It was a struggle in the first half Rating: 4/10
Andy Holdsworth Again at left-back, made a fine early block to deny Boulding as Town came under pressure. Limped off suffering a groin injury Rating: 4/10
Nathan Clarke Off at half time because of a groin injury with Town having been ripped to shreds in the first period by Barnsley Rating: 4/10
Efe Sodje Gave the ball away for Boulding's goal but played better in the second half. Wrestled a fan off the pitch! Rating: 4/10
Chris Brandon Too often spare in the first half but played a great pass for Beckett to earn the penalty. Booked and suspended Rating: 4/10
Tony Carss Moved to left-back in a reshuffle following the Holdsworth injury and much more involved from that wide position Rating: 4/10
Jon Worthington Looked much happier when pressing forward in the second half and tried his luck with several shots. Grafted throughout Rating: 5/10
Danny Schofield The only Town player to have a shot in the first half, he was taken off to get Fowler into the action. Yellow carded Rating: 4/10
Pawel Abbott Not a performance to remember but took his tally for the season to 18 and was also unlucky to hit the bar Rating: 4/10
Luke Beckett Received no service in the first half and denied by a brilliant Colgan save in the second in a decent debut display Rating: 6/10
Spotlight on the ref:
TOWN will hope they don't see Berkshire official Trevor Kettle for a long time to come, and the home side are probably saying the same thing. He had a dreadful match and was far too fussy all the way through.
At one stage, no-one knew what was going to happen next, so inconsistent were his decisions. Pawel Abbott was lucky to get a second chance with his penalty after what appeared a good first save by Colgan, while Paul Rachubka was lucky not to see red for his late barge on Chopra which conceded a penalty
Barnsley: Turnbull; Hassell, Williams, Reid, Vaughan; Shuker (Colgan, Gkp, 50), Burns, Kay, McPhail (Austin 82); Chopra, Boulding (Carbon 71).
Subs not used: Stallard, Wroe.