Graeme Jones' men were up against it from as early as the fourth minute when Marley Watkins bundled home from close range.
City were worthy winners against a disappointing Hatters side, with Lee Johnson's men even having the luxury of being able to miss a first-half penalty.
The loss saw Luton drop to second bottom in the Sky Bet Championship, with Barnsley edging above them thanks to a 0-0 draw at Swansea City.
Here's how the Luton players rated in the Ashton Gate reverse.
The loss saw Luton drop to second bottom in the Sky Bet Championship, with Barnsley edging above them thanks to a 0-0 draw at Swansea City.
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