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.
5. Harry Cornick 5
Was a willing runner but all too often was given lost causes to chase. Had Town's best chance and was unlucky to see it cleared off the line | freelance Photo: Liam Smith
6. Pelly-Ruddock Mpanzu 4.5
Beaten in the air by Watkins and needed a Shea stop to get him out of bother, but provided the assist for Cornicks chance and then blazed a 20-yarder agonisingly wide | freelance Photo: Liam Smith
7. James Collins 4.5
The striker had to feed off scraps the entire game and there was the usual effort, running and chasing, but not a sniff of goal. He collected his 8th yellow card of the campaign | freelance Photo: Liam Smith
8. Luke Bolton 3
Niclas Eliasson had him to toast and twice ghosted past him to deliver dangerous crosses for Watkins. He's finding it a difficult transition from an attack-minded pacey winger to full back | freelance Photo: Liam Smith