Peterborough 2 (Washington 45, Maddison 69)
Reds 1 (Cole 15, Bailey s/o 77)
Barnsley were undone by two contrasting goals at Peterborough - a defensive error and a sensational free-kick overturned the Reds' lead courtesy of Devante Cole.
To add insult to injury, James Bailey will serve a one-match suspension after picking up two yellow cards in the second half.
Ross Turnbull had to be quick off his line as he made a brilliant sliding tackle 25 yards from his goal to deny what looked to be a certain Posh goal as Washington raced through.
At the other end, Conor Hourihane tried his luck from a 25-yard free-kick but his effort deflected wide off the wall for a corner on four minutes.
With 15 played, the Reds enjoyed their first proper passage of play and it resulted in a fantastic goal. Patient, neat play saw Bree swing in a brilliant cross from the right, and Devante Cole showed great technique to volley home from nine yards.
Sam Winnall created himself a decent chance after cutting in from the left but he cracked a low effort into the side netting as Barnsley had the bit between their teeth.
Posh's response was to hit the outside of Turnbull's left-hand upright and it was Washington again for the hosts on 19 minutes who had managed to dig out the shot.
Christian Burgess wasted a decent chance as he blazed his free header wide on 35 minutes following a good corner from the right. Posh had been controlling the majority of play and looked determined to claw a goal back.
It looked like a change was enforced for Posh as Burgess was replaced by Santos six minutes before the break.
Barnsley's next chance was for Conor Hourihane on 41 minutes as Bree's cross once more cause havoc and Cole stepped over the ball to allow Hourihane a shot that deflected wide.
The equaliser came for Posh on 45 minutes as the Reds failed to clear the danger from the edge of the area when they had the chance. Instead, Washington was allowed a free shot of goal and he didn't make a mistake from 18 yards.
Space opened up for Conor Hourihane on 51 minutes 30 yards out but the Reds' leading scorer's effort was always rising as it sailed over the bar.
It took some last-ditch defending on 55 minutes to keep the hosts out as Cranie and Nyatanga got blocks in to thwart Newell as the Posh corner count continued to rise.
When the flag didn't go up on Washington, the Reds had to clear their lines but Smith got a shot in that Turnbull had to save well on 61 minutes.
From one end to the other, Ramage went close on the spin but Posh countered and Taylor went one-on-one with Turnbull only to be denied by the big 'keeper on 64 minutes.
Maddison sent in a lovely curling effort from 25 yards but it appeared Turnbull had it covered as it sailed past the far post. The game was stretched and the Reds needed to take the sting out of the game.
On 69 minutes an incredible 30-yard free-kick from Maddison found the top corner to make it 2-1. It was great technique by Maddison as he side-footed a thunderous effort into the top corner.
Already a goal behind, the Reds' task was made even harder when Bailey picked up a second booking and was giving his marching orders on 77 minutes.
The Reds were leaving themselves exposed at the back as they searched for an equaliser with 10 men. Leroy Lita replaced Luke Berry on 89 minutes.
In stoppage time Maddison could have added a third but Turnbull made a brilliant stop after the Posh man had danced into the box.
Barnsley: Turnbull, Berry (Lita 89), Nyatanga, Cranie (C), Hourihane, Winnall (Digby 79), Williams (Hemmings 75), Ramage, Bree, Bailey (s/o 77), Cole.
Subs: Davies, Brown, Dudgeon, Treacy.
Peterborough: Alnwick, Bestwick, Baldwin, Burgess (Santos 39), Smith, Newell, Payne (C), Anderson (Ferdinand 90), Maddison, Taylor (McEvoy 78), Washington.
Subs: Grant, Mendez-Laing, James, Oztumer.