The Reds are dealt a blow in Burton to their automatic promotion hopes as they fall to first defeat of 2019.
Reds Head Coach, Daniel Stendel made just the one change to his starting XI with Spanish full back Dani Pinillos returning to fitness and the first team in place of Ben Williams who dropped down to the bench.
The game got off to a disastrous start for the Reds, going behind inside five minutes when after great wing-play from Marcus Harness, his ball was hit first time by Scott Fraser and with Adam Davies in the Barnsley goal unable to hold the effort, in came Jamie Allen to slot home into an empty net.
Strong claims for a Brewers penalty were turned down by referee Michael Salisbury, with Liam Boyce falling in the box. The striker was booked for simulation.
The Reds were lethargic and struggling to complete passes, and only a tame Cam McGeehan shot from range was troubling the hosts' goal in the opening 20 minutes.
Lucas Akins finished in style but the pass from Stephen Quinn was timed a fraction late, offside given and Barnsley could breathe again.
There was very little to report for the rest of the first half, with a penalty appeal waved away the only real moment for Barnsley, as Jake Buxton looked to have stopped a cross with his arm.
HALF TIME: Burton 1-0 Barnsley
Straight from the restart the home side should have doubled their advantage but Boyce tried to lob Davies when a simple finish would have sufficed, and the Reds' skipper stopped him.
Harness wasted a glorious chance on the hour mark, firing wide after some fine play by the impressive Akins through the middle.
Stendel introduced Mike Bähre and Callum Styles immediately aferwards with Jacob Brown and Mama Thiam off, and the Reds did start to see more effective attacking moves, with Ryan Hedges forcing 'keeper Collins into a low save and then Cauley Woodrow seeing his header from the corner go just over the crossbar.
But then came the sucker punch as Harness's through ball beat the offside trap and this time Boyce finished low and hard and beyond Davies to double the Brewers' lead.
There was a late appearance for Victor Adeboyejo and then on 85 minutes a penalty from nowhere, to the Reds. We've still no idea why it was awarded, but up stepped Woodrow to fire home his 16th of the season and breathe life into the contest.
But the game was put to bed as we entered stoppage time. With the Reds attacking at will, they were caught on the break again and Harness scored from a couple of yards out to make it 3-1.
A first defeat in 21 matches and with other results going against us it wasn't a great day for Stendel's side.
FULL TIME: Burton 3-1 Barnsley
Davies, Cavaré, Pinnock, Lindsay, Pinillos, Brown, McGeehan, Mowatt, Thiam, Hedges, Woodrow.