Two goals from veteran striker Nicky Forster helped Russell Slade's side to a win at Brunton Park, ensuring Carlisle's stop-start season continued.
But Thirlwell believes they can soon get their campaign back on track if they quickly erase the memory of the loss.
"I turned up, as I'm sure everyone else did, expecting to win the game," he told United's official website.
"The key is not too get too down when you lose because who is to say you won't go on to win your next four or five games out of your next set of fixtures?
"We've shown already that it can be done, so we just have to keep going."