Cardiff went ahead in impressive style with two goals in three minutes to stun Andy Ritchie's play-off heroes.
Ironically it was midfielder Stephen McPhail, one of Ritchie's stars of the May play-off victory, who helped create the opener.
McPhail , who controversially quit Oakwell in the summer for a move to Ninian Park, flicked a deft ball for Riccardo Scimica and his angled pass sent in another ex-Barnsley hero Michael Chopra.
The former Newcastle striker slid in an inch-perfect pass for Joe Ledley whose pace put him into space and he had a simple finish from point-blank range to easily beat Nick Colgan.
Barnsley had barely got their breath back when Ledley, wide on the left, crossed a low ball that fell perfectly for striker Steve Thompson who met it with his left foot and smashed a low volley just inside Colgan's right-hand post as the keeper dived at full stretch.
The setback sparked Ritchie's side and Paul Heckingbottom's downward header triggered a 22-yard drive from striker Paul Hayes who smashed his shot wide of the target.
On the half-hour a cross from Bobby Hassell found new signing Michael McIndoe but his header was a tame effort straight at the keeper.
A minute later though Barnsley were back in the game with a bang when Brian Howard pulled one back in a style to match the Cardiff strikes.
Heckingbottom crossed from the left and Howard, who had found space, chested down and unleashed a fierce left-foot shot that gave Neil Alexander no chance.
After the break Paul Hayes went close with a 25-yard free-kick that dipped over the bar after he squeezed it over the Cardiff wall.
Cardiff threatened again after 53 minutes when Ledley hammered an unstoppable 20-yard shot that hit the post before follow-up efforts from Thompson and Chopra were blocked.
And a minute later Scimeca went down in the area after a rash challenge from Hassell but Darren Purse's shot from the resulting penalty was well saved by Colgan. His follow-up was blocked.
Marc Richards should have levelled for the home side after 73 minutes but when Hayes crossed Richards lifted his shot over the keeper but hit the bar.
A late shot from Scimeca brought a great save from Colgan.