The Reds began November with a chastening defeat away at a bitterly cold Cardiff on Tuesday night.
It was a really tough watch in Wales for the Reds, as Valérien Ismaël saw his new side lose for the first time. And pretty comfortably.
The hosts took an early lead when a cross from the left wasn't dealt with by Michal Helik inside the box, the ball fell kindly for Junior Hoilett and the experienced forward turned to steer home beyond Jack Walton for 1-0.
Robert Glatzel glanced a header just wide from an inviting Harry Wilson cross before then heading straight at Walton a moment later, as the Reds struggled to cope with the direct nature of their opponents' football.
There was little of note to report on from a Barnsley perspective in the opening 45, but after Elliot Simoes was replaced on 40 minutes by Clarke Oduor, a first opening arrived, as Matty James clipped a great ball over the top that Conor Chaplin latched onto, but his shot was saved by the onrushing Alex Smithies who then blocked Patrick Schmidt's follow-up.
Barnsley were made to pay as Wilson was sliced down by Helik inside the box right on half time and up stepped Joe Ralls to double the home side's lead from the spot.
HALF-TIME: Cardiff City 2-0 Barnsley
There was better intensity about the Reds' play in the second half but the damage had already been done.
Oduor had to be quickly across to thwart Wilson with a great slide tackle inside the box before Patrick Schmidt saw his header tipped over the bar at the other end. That was his last action of the game, making way for Victor Adeboyejo on 62 minutes.
It became very scrappy for a good 10 minutes before Chaplin tried an effort from range that whistled wide.
The hosts though made it 3-0 in the 76th minute when the best player on the night, Wilson skipped into space on the edge of the box before curling home into the top corner.
Aapo Halme came on for the last 10 minutes as James made way, but the Reds were well-beaten by now. They never stopped going, but it was a bad night in the Welsh capital as they succumbed to their first defeat in a month.
FULL-TIME: Cardiff City 3-0 Barnsley
Walton, Sollbauer, Helik, Andersen, Frieser, Mowatt, James (Halme), Styles, Chaplin, Schmidt (Adeboyejo), Simoes (Oduor).
Unused: Collins, Kane, Miller, Thomas.