The Reds were comfortably second best for the first 60 minutes, conceding from a set piece in the first half then from a bad Adam Davies error at the start of the second. But Jacob Brown inspired the comeback, assisting goals from Mamadou Thiam in the 70th minute and substitute Kieffer Moore in the 78th.
A win would have seen the Reds overtake second-placed Portsmouth who lost 3-2 at leaders Luton Town with former Barnsley player George Moncur netting the winner. The third-placed Reds are a point off the two automatic promotion places.
Daniel Stendel changed from 4-4-2 to 4-5-1 as he dropped top-scorer Moore and replaced him with central midfielder Kenny Dougall. Mike Bahre returned to the bench after injury with Ryan Hedges dropping out of the squad.
The visitors were disappointing in the first half as they struggled to achieve the control Stendel wanted with an extra man in midfield. The Us were the better side and hit the crossbar twice either side of their goal.
The first big chance fell to Barnsley when Brown cleverly won a free-kick on the right wing which was taken low by Alex Mowatt to Cameron McGeehan whose shot from eight yards out was kept out well by goalkeeper Simon Eastwood.
Oxford then came close to taking the lead midway through the first half but Gavin Whyte’s 20-yard strike was impressively tipped onto the bar by goalkeeper Davies.
The opening goal came on 25 minutes when slack marking from a right-wing corner allowed Rob Dickie to head across goal for Josh Ruffels to nod in from two yards out.
It was almost 2-0 two minutes later when Davies rushed out of his box but was beaten to the ball by Jamie Mackie whose 30-yard lob hit the underside of the crossbar and the line before Davies got back to brilliantly deny James Henry’s rebound.
Dickie then headed over from a Ruffels cross but Barnsley finished the half strongly with McGeehan forcing Eastwood into another good save with a low 20-yard shot then Liam Lindsay headed a Mowatt corner over from close range.
Stendel replaced Dougall with Moore at half-time as he reverted to 4-4-2 but they were under pressure straight after the restart with Curtis Nelson hitting the bar with a header from a corner, with Davies seemingly getting fingertips on the ball.
It was 2-0 on 48 minutes when a long ball led to a terrible mix-up between Lindsay and Davies who hesitated then could to grasp the ball under pressure from Mackie who barged past him and tapped into the empty net.
Davies then came up with two excellent saves in the next ten minutes, pushing Jordan Graham’s low long-range shot out of his bottom left corner then superbly pushed over Dickie’s header from a Brannagan corner.
Thiam halved the deficit on 70 minutes, smashing in a low ten-yard shot after a good run and pull-back on the left side by Brown, but then the Frenchman was instantly substituted for Bahre.
Brown also assisted the equaliser eight minutes later when he again raced down the left wing and sent in a low cross which a sliding Moore fired into the top right corner.
Barnsley looked the most likely winners but, in injury-time, Brown had a shot from a tight angle beaten away by Eastwood then Moore headed over a Mowatt free-kick under pressure from defenders.
Barnsley team: Davies; Cavare, Pinnock, Lindsay, B Williams; Brown, McGeehan, Dougall (Moore HT), Mowatt, Thiam (Bahre 71mins); Woodrow (Green 61). Unused: Greatorex, Jackson, Pinillos, Adeboyejo. Yellow cards: Thiam, Dougall, Lindsay, Williams, Mowatt. Goals: Thiam 70, Moore 78.
Oxford: Eastwood; Hanson, Dickie, Nelson, Ruffels; Whyte, Brannagan, Mousinho, Graham (Garbutt 81); Henry (Kashi 854), Mackie. Subs: Stevens, Carruthers, Long, Sykes, James. Yellow cards: Nelson. Goals: Ruffels 25, Mackie 48.
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