Barnsley's 12-game unbeaten run came to an with a 2-1 home loss to local rivals Sheffield Wednesday.
Jordan Rhodes, the former Oakwell academy player, netted either side of half-time to put his side 2-0 up.
Carlton Morris replied in the 78th minute but the Reds were beaten on a day when they put in their worst performances for weeks.
Barnsley remain fifth, five points clear of the sides outside the play-offs but seventh-placed Bournemouth now have a game in hand on them.
Valerien Ismael made no changes from the side that won 3-1 at Wycombe Wanderers on Wednesday. Herbie Kane was not on the bench, with Jasper Moon replacing him.
Barnsley wore special training tops with the message 'keep fighting Bayley' dedicated to Bayley Hassell – the under 18s player and son of former Oakwell hero Bobby Hassell – who is fighting cancer, as announced this week.
Wednesday had to make a change in their starting line-up after goalkeeper Keiren Westwood was injured in the warm-up and replaced by former Barnsley loanee Joe Wildsmith.
Michael Sollbauer should have opened the scoring in the third minute but he fired over the bar from close range at the back post after a left-wing Alex Mowatt corner was flicked on at the near post by Daryl Dike.
The Reds dominated the opening 15 minutes but then lost their way, with Wednesday having the better of the rest of the half.
The visitors should have taken the lead in the 20th minute when goalkeeper Brad Collins rushed out to the edge of his box and missed the ball then Jordan Rhodes fired wide of the nearly empty goal on the left of the box.
Barnsley had the ball in the back of the net when Cauley Woodrow bundled home from close range, following another right-wing Mowatt corner, but the referee ruled that goalkeeper Joe Wildsmith had been fouled while dropping the ball. Barnsley then appealed for a penalty after Dike went down in the box under pressure from Tom Lees.
The visitors took the lead in the 39th minute minute when Barry Bannan's cross from the left wing was headed in by Rhodes from close range.
Woodrow had Barnsley's only shot on goal of the first half in the 44th minute but the 25-yard effort was easily held by Wildsmith.
Ismael made a triple change at the break, with Sollbauer, Romal Palmer and Dominik Frieser replaced by Toby Sibbick, Aapo Halme and Carlton Morris.
The visitors doubled their lead seven minutes into the second half when Callum Styles was tackled in his half by Liam Palmer and Wednesday had two men clean though, with Josh Windass squaring for Rhodes to tap into an open goal.
Julian Borner then headed over a right-wing corner by Bannan then, at the other end, Dike shot straight at the goalkeeper from ten yards after Morris had brought down a Brittain cross from the right.
Windass could have made it 3-0 when a long ball over the top put him in in on the left of the box but he screwed his shot well wide with only Collins to beat.
Morris pulled one back with 12 minutes left when, after a Brittain long throw fell to him, his 15-yard deflected shot looped into the left of the net with the goalkeeper stranded.
Mowatt then curled a 25-yard free-kick just over the bar in the 87th minute.
Barnsley (3-4-3): Collins; Sollbauer (Sibbick HT), Helik, Andersen; Brittain, Mowatt, Palmer (Halme HT), Styles; Frieser (Morris HT), Dike, Woodrow (Chaplin 68mins).
Unused: Collins, J Williams, Oduor, Adeboyejo, Moon.
Goals: Morris 78.
Wednesday (3-4-3): Wildsmith;, Lees, Börner, Urhoghide, Pelupessy, Palmer, Bannan, Paterson, Reach; Windass (Green 84mins) Rhodes.
Unused: Jackson, Brennan, Galvin, Penney, Hunt, Brown, Harris, Kachunga
Yellow cards: Lees, Borner, Paterson.
Goals: Rhodes 39, 52.