Barnsley gained their first win over Sheffield Wednesday since 2009 with a 2-1 victory at Hillsborough on Saturday.
The Reds conceded in the fourth minute due to a defensive mix-up but Cauley Woodrow and Dominik Frieser put them 2-1 up at half-time, then they held on in an ugly second half battle.
They have now won seven of their 11 games under Valerien Ismael and are 13th in the table, six points off the top six and 12 above the bottom three. They are 16 points and 13 places ahead of bottom club Wednesday.
Valerien Ismael made one change from the side that beat Wycombe Wanderers 2-1 at Oakwell on Wednesday, with Frieser replacing the benched Luke Thomas.
The Reds made a disastrous start as, in the fourth minute, Jack Walton ran to the edge of his box but – following hesitation between him and his defenders – was beaten to it by Josh Windass who rounded the goalkeeper and tapped into the empty net.
But Barnsley responded well and, after a period of pressure without carving out clear chances, they levelled in the 14th minute. Matty James' corner from the left was flicked on at the near post by Mads Andersen, missed by goalkeeper Joe Wildsmith and headed in on the line by Woodrow.
Wednesday continued to attack mainly through long balls and set pieces, with debutant Chey Dunkley heading over a long throw by Callum Paterson under pressure from defenders.
The visitors took the lead late in the second half when, after good work on the right wing involving the impressive duo Callum Brittain and James, the ball was fizzed towards Chaplin who, 25 yards from goal, clipped an excellent pass over the home defence into the path of Frieser. The Austrian was clean through and beat Wildsmith for his second Barnsley goal.
Wednesday began the second half well and tested Walton twice in the first five minutes. Former Barnsley player Kadeem Harris had a shot from the edge of the box on the right but Walton did well to dive to his right to push it wide. The Reds stopper also pushed a powerful 20-yard Windass effort into the air soon after.
Barry Bannan also blazed over from 30 yards while, at the other end, Chaplin tapped in from a Brittain cross but it was given offside.
Barnsley's first shot on target after the break came from Woodrow who took a fine touch then let fly from 25 yards but his low effort was turned around the bottom right corner by Wildsmith.
Wednesday half-time substitute Joey Pelupessy looked set to level when he received a pass from Harris in the box but slipped and totally missed the ball.
The visitors should have gone 3-1 up in the 73rd minute. Styles and Woodrow worked the ball superbly from the left wing into the box where substitute Luke Thomas' heavy touch rolled perfectly to Styles who smashed over from six yards out.
The hosts came extremely close to levelling in the 78th minute when Pelupessy shot from outside the box and Walton brilliantly tipped it onto the crossbar then it hit him in the back and bounced onto the post. That was the last real chance of the game as Barnsley held on to win.
Barnsley (3-4-3): Walton; Sollbauer, Halme, Andersen; Brittain, Mowatt (Palmer 90mins), James (Kane 67), Styles; Frieser (Thomas 67), Woodrow (Miller 86), Chaplin (Adeboyejo 67). Unused: Collins, Helik, Oduor, Schmidt. Goals: Woodrow 14, Frieser 39.
Wednesday (3-4-3): Wildsmith; Dunkley, van Aken (Pelupessy HT), Lees; Odubajo (Palmer 66mins), Iorfa (Rhodes 84), Bannan, Paterson (Brown 84), Reach, Windass, Harris.
Unused: Dawson, Dele-Bashiru, Penney, Hunt, Kachunga.
Goals: Windass 4.