Poya Asbaghi's time in charge of Barnsley began with a 2-0 loss at home to Swansea City on Wednesday which left them six points adrift of safety.
The visitors netted in the 74th and 80th minutes of a game of few clear-cut chances but one in which Swansea dominated possession and looked to have extra quality.
The Reds remain second-bottom in the Championship with 11 points from 19 games.
Asbaghi made three changes to the side that lost at Fulham on Saturday. Mads Andersen dropped out of the squad with illness while Carlton Morris and Toby Sibbick dropped to the bench. Callum Brittain returned from suspension while Jasper Moon and Devante Cole also came back in. Brittain played at right-back, with Jordan Williams on the left, in a 4-3-3 with Romal Palmer less advanced than on Saturday in a 4-2-3-1.
Nothing of note happened in the first 45 minutes, with neither side having a shot on or off target. Swansea dominated the ball, with 81 per cent possession, but Barnsley looked compact in their shape and well-organised without offering much going forward.
Just before the break, a left-wing cross was headed at the back post by Ethan Laird but blocked by Callum Styles then, seconds later, Laird's deflected low cross from the right fell to Joel Piroe who fired wide of the bottom right corner 12 yards out when he should have scored.
Barnsley had their first shot on goal eight minutes into the second half when Michal Helik released Cole on the right wing and he beat Kyle Naughton before crossing for Cauley Woodrow who, under pressure from a defender ten yards out, sliced into the ground and the goalkeeper caught easily.
Asbaghi then brought on Morris and Aaron Leya Iseka for Cole and Frieser, just before Josh Benson curled a 25-yard free-kick over.
Swansea's first shot on goal was in the 69th minute when Laird's header from the right of the box was easily caught by Collins.
The breakthrough came four minutes late when substitute Ryan Manning crossed low from the left and fellow replacement Olivier Ntcham swept in from six yards out after getting away from Styles.
Asbaghi responded immediately by bringing on tall striker Obbi Oulare for his home debut in place of midfielder Palmer as Barnsley adopted a 4-2-4 formation. Oulare was booked for a wild late tackle.
It was 2-0 on 80 minutes when Jamie Paterson received the ball from Piroe and, exploiting major gaps in the Barnsley side, drove into the penalty area and fired into the bottom right corner.
Barnsley (4-3-3): Collins; Brittain, Moon, Helik, J Williams; Styles, Benson, Palmer (Oulare 77mins); Cole (Morris 57), Woodrow, Frieser (Leya Iseka 57mins).
Unused: Walton, Gomes, Sibbick, Adeboyejo.
Yellow cards: Oulare.
Swansea (3-5-2): Hamer; Bennett, Cabango, Naughton; Laird, Smith, Downes (Ntcham 64mins), Grimes, Bidwell (Manning 71); Paterson, Piroe.
Unused: Benda, Cullen, Latibeaudiere, Walsh, Williams.
Yellow cards: Naughton, Bennett, Smith.
Goals: Ntcham 74, Paterson 80.