Rovers ran out 3-0 winners with a brace from Kieran Sadlier plus a Ben Whiteman strike.
Ferguson felt the timing of Rovers' goals were key and helped them halt Peterborough's progress.
"There was never three goals in that game," he said.
"But we have to take it on the chin and move quickly towards the Rotherham game now. It's a very busy period.
"We have to dust ourselves down and go again.
"I know it's a cliche but goals change games and the second goal changed the game because we were in total command of the game at that point.
"I think we only had four shots against us on target and we've lost 3-0. And we've had 18 shots at their goal.
"But it's the scoreline that matters.
"It's a difficult one to take in terms of it being 3-0, which looks really damaging.
"Congratulations to Doncaster, it's a good result for them and they definitely celebrated like it was."