Back in November it was the first round of the FA Cup when a late goal from striker Junior Agogo proved decisive and in this League Two encounter it was a soft goal 11 minutes from time that did the trick.
When Grimsby winger Andy Parkinson brought down a Rovers player wide on the left he received a yellow card for his pains.
But to add insult to his injury a free-kick taken by Rovers midfielder Chris Carruthers somehow found its way into the net through a number of legs.
A soft goal like that was always going to decide a tense encounter in which not a clear cut chance was created at either end.
For Bristol, striker Richard Walker shot wide earlier on and Grimsby's only effort on target was a header on the hour by striker Gary Cohen which was easily saved.
After the high spot of a 4-1 midweek win against Rochdale, this defeat, Grimsby's fifth at home this season, brought them down to earth with a bump.
It was a welcome return to Grimsby for Rovers' director of football Lennie Lawrence and it was Rovers' second successive 1-0 away win in a week.
It puts them in good heart for their midweek FA Cup second round replay at home to Port Vale.
For Grimsby, meanwhile, they will be anxious to atone for this set back with three of their next four games on the road apart from the Lincolnshire derby with Lincoln City on December 28.
An improved crowd from midweek went home disappointed and, although they did their best to get behind the team, there was precious little for them to get excited about.