Cauley Woodrow put the Reds ahead then, after the hosts made it 1-1 at half-time, Kieffer Moore, Mamadou Thiam and Cameron McGeehan secured the win in the second half.
Barnsley remain fifth, but just five points behind the leaders Portsmouth who suffered a shock loss at Oxford United.
Daniel Stendel kept the same team which beat Bradford City 3-0 a week previously. There were two changes on the bench where Dani Pinillos and new signing Jordan Green replaced the injured Mike Bahre and George Moncur who was sold to Luton Town yesterday.
Shots from 20 yards by both McGeehan and Thiam forced home goalkeeper Aaron Ramsdale into good saves diving low to his right.
The stopper was eventually beaten in the 19th minute when the Dons could not clear a left-wing corner and Woodrow smashed into the top left corner from 12 yards out.
Alex Mowatt almost made it 2-0 four minutes later when Thiam’s clever ball released him in the box but Ramsdale made another good save to tip the 15-yard effort over the bar.
The hosts gradually got back into the game and eventually levelled with their first shot on target on 37 minutes as Joe Pigott glanced a header in from Andy Barcham’s right-wing free-kick.
Wimbledon almost took the lead through a powerful Will Nightingale volley from 25 yards but Davies tipped the ball over the bar. Jake Jervis then incredibly missed from four yards out with the goal gaping after Pigott’s shot was deflected straight to him. The Reds suffered a blow when Woodrow had to come off injured and was replaced by defensive midfielder Kenny Dougall who almost scored his first Barnsley goal but his lofted 20-yard volley was tipped over by the impressive Ramsdale in first half injury-time.
The Dons had the first chance after the interval as Deji Oshilaja fired a shot across the face of goal from the right of the box. But it was the visitors who took the lead eight minutes into the second half when Mowatt crossed from the right wing and Moore headed into the bottom left corner.
Mowatt then headed a Ben Williams cross straight at Ramsdale but it was 3-1 midway through the second half when Moore skipped past a defender on the left wing and saw his cross break to Thiam who smashed into the top left corner from ten yards. Barnsley thought they had a fourth when a header was headed off the line onto the underside of the bar but the referee decided it had not crossed the line. Moore then fired straight at Ramsdale from 15 yards after a good run and pull-back by Mowatt before Thiam curled a 25-yarder just wide of the top right corner. Liam Lindsay also headed wide from a corner.
The rout was completed in the 89th minute when a left-wing cross by Thiam was headed down by Jacob Brown to McGeehan who fired in a low shot from eight yards.
Barnsley: Davies, Cavare, Pinnock, Lindsay, B Williams (Pinillos 67mins); Brown, Mowatt, McGeehan, Thiam; Woodrow (Dougall 42), Moore (Adeboyejo 81). Subs: Greatorex, Jackson, Green, Hedges. Yellow cards: Pinnock, Williams. Goals: Woodrow 19, Moore 53, Thiam 65, McGeehan 89.
Wimbledon: Ramdsale; Watson, Kalambayi, Thomas, Seddon; Pinnock, Oshilaja, Nightingale, Barcham (Connolly 60mins); Jervis, Pigott (Wordsworth 67). Subs: McDonnell, Wagstaff, Hartigan, Garratt, Wood. Goals: Pigott 37.
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