Le Fondre, who joined the Millers from League Two rivals Rochdale last week, scored from the penalty spot on his full debut to help sink lowly Town.
Robins said: "Adam became more and more influential as the game wore on and was key to the way we played in the second half especially.
"It was good for him to get on the scoresheet on his debut and there is more to come from him.
"Overall, I was delighted with three points on the road and thought we played well enough to deserve the win. In fairness to Grimsby,
they pressed us well but I was pleased we reacted to that, especially when we were pegged back to 1-1. It was a new strike partnership for us and as the game wore on, the link-up play between Tom Pope and Adam grew.
"We played some decent stuff, the only negative for us is that Ian Sharps has picked up a groin strain and Jamie Green also had to go off injured. But overall, it was a pleasing night for us."