Manager Gary Johnson urged his Robins to learn the lessons of defeat – after conceding an off day had cost his team at Port Vale.
Kevin Dawson marked his return to action with a stoppage time goal.
But it was no more than a consolation as Tom Pope (2) and Ben Whitfield won the game for the Valiants.
“It was an off day,” said Johnson. “They had a game plan and it beat us. The long ball and Tom Pope getting lots of flick-ons; it gave them momentum, they got runners in and we couldn’t get up the other end.
“The lads are gutted. They know they haven’t performed and we’ve got to learn from this.
“We have still got a young and inexperienced team generally and they have got to learn from days like this.”
“It’s a lesson for our centre halves because there are some strong centre forwards in this league,” he added.
“It’s also a lesson for our centre forwards, to see how much they can affect the game if they are strong and winning everything. It’s a lesson for everyone.
“We knew they weren’t going to be a bad team. We knew they would be on the front foot if they could, and we didn’t play well enough to put them on the back foot."