IN-FORM Carlton Morris scored for the third match running to seal a third successive win for Barnsley, who are now just four points off the Championship play-off places.
Just as against Blackburn Rovers on Wednesday, the 25-year-old came off the bench as part of a triple substitution by head coach Valerien Ismael – and provided the breakthrough goal after 67 minutes.
It was enough to earn a deserved success for the tenth-placed Reds, who beat Brentford to kick-off the victorious run and are now unbeaten in five Championship games.
Bristol City parted company with head coach Dean Holden in the wake of Tuesday's home loss to Reading, but caretakers Paul Simpson and Keith Downing couldn't stave off a sixth successive league defeat for the West Country side.
Ismael made two changes from the team which started Wednesday's 2-1 home win over Blackburn Rovers, with Michael Sollbauer replacing Toby Sibbick in the back three and Daryl Dike coming in for Victor Adeboyejo up front.
Meanwhile, centre-back Aapo Halme, back from injury and who last played in mid-December, was named among the substitutes.
The Reds, as usual going 3-4-3, carved out the first decent chance of the contest on 15 minutes, when centre-back Michael Helik put a Conor Chaplin delivery over from close range.
Dike, the powerful American on loan from Orlando City, was making his presence felt, and after poking an effort just too high, couldn't quite make contact with a teasing cross from wing-back Callum Brittain.
City's first opportunity arrived after 35 minutes, but Kasey Palmer was wide from a flick by Famara Diedhiou, who then had a long-range shot comfortably collected by Barnsley goalkeeper Brad Collins.
Ismael has a liking for player rotation, and on 55 minutes, introduced Morris, Jordan Williams and Adeboyejo for Chaplin, Styles and Cauley Woodrow.
Home keeper Daniel Bentley had managed to thwart Brittain, but was powerless to prevent Morris putting Barnsley in front after Mowatt's corner was touched on by Sollbauer, leading to a frantic scramble.
Bristol City: Bentley, Mariappa, Kalas, Moore, Hunt, Vyner (Paterson, 69), Lansbury (Bakinson, 58), Palmer, Sessegnon (Nagy, 76), Semenyo (Wells, 69), Diedhiou. Unused: Pearson, Bell, Towler, Massengo, O'Leary.
Barnsley: Collins, Sollbauer (Sibbick, 75), Helik, Andersen, Brittain, Palmer, Mowatt, Styles (J Williams, 55), Chaplin (Morris, 55), Woodrow (Adeboyejo, 55), Dike (Frieser, 82). Unused: Kane, Morris, Oduor, Halme, Walton.
Referee: James Linington (Isle of Wight).