Ryan Garry stooped low to head a Lee Bradbury cross past Andy Warrington and into the far corner to register the only goal of the game in the 45th minute.
Robins said: "Credit to them. They made it difficult for us and stifled us to a large extent.
"Steve Fletcher and Brett Pitman created confusion in our defence, and really we should have dealt with the goal better than we did.
"We can pass it (the ball) as well as we can, but we've one or two new players in the side and have still got a lot of work to do."