Barnsley's run of four straight home wins came to an end with a 2-0 loss at home to second-placed Swansea City.
The visitors had been second best in the first half but took the lead just before the break then doubled it early in the second half after a terrible mix-up between Mads Andersen and Michal Helik.
The Reds are now tenth, six points off the play-off places, while they have lost their last two league games against the current top two.
Valerien Ismael made two changes from the team that beat Tranmere Rovers in the FA Cup last week. Jack Walton returned in goal while Victor Adeboyejo came in for Dominik Frieser. New signing Carlton Morris started on the bench.
The first chance of the game fell to Adeboyejo in the 11th minute when away defender Ben Cabango slipped over and the striker ran onto a Herbie Kane pass then blasted over from just outside the box when he could have passed to Cauley Woodrow on his right.
Adeboyejo tested the goalkeeper with a powerful shot from the right of the box at a very tight angle which was beaten away and, from the resulting corner, Conor Chaplin saw a shot blocked.
At the other end, Walton had to claw away a long throw by Connor Roberts which Jake Bidwell tried to get on the end of. A corner from the right then seemed to hit Andre Ayew and go wide from five yards out.
Styles tested goalkeeper Freddie Woodman with a low 25-yard shot in the 39th minute but it lacked power and was easily gathered.
But the visitors took the lead in first half injury-time when another Roberts long throw from the right was met by Cabango whose impressive header looped into the top left corner. Michael Sollbauer had been left marking Sollbauer and ex-Red Korey Smith but the former was free to nod the ball into the net.
The Swans were on top early in the second half, with Roberts firing a vicious volley just wide of the right post from outside the box.
It was 2-0 on 56 minutes when a hopeful header forward should have been cleared but Andersen headed it into Helik as they bumped into each other then the ball rolled to Jamal Lowe who went clean through on goal and fired past Walton.
Ismael brought on Morris for his debut and Romal Palmer, with Conor Chaplin and Herbie Kane taken off.
Woodrow headed wide from a cross by Brittain who almost scored his first Barnsley goal with a sensational 25-yard strike but Woodman did well to claw it out of the top left corner. Brittain then beat a man on the edge of the and fired over.
At the other end, Walton touched wide a right-wing free-kick by Roberts which had looked destined for the top right corner.
Barnsley (3-4-3): Walton; Sollbauer (Sibbick 84mins), Helik, Andersen; Brittain, Mowatt, Kane (Palmer 63), Styles; Chaplin (Morris 63), Woodrow, Adeboyejo (Thomas 84). Unused: Collins, Oduor, Schmidt, Moon, Frieser. Yellow cards: Andersen.
Swansea (3-5-2): Woodman; Naughton, Cabango, Guehi; Roberts, Smith, Fulton, Grimes, Bidwell; Lowe, Ayew. Unused: Hamer, Latibeaudiere, Manning, Byers, Dhanda, Cooper, Routledge, Garrick, Cullen.. Goals: Cabango 45+1, Lowe 56.