With a strong wind and driving rain in their faces, the visitors defended for their lives and conceded only once to a deflected header from substitute Wes Burns eight minutes from time.
Cotterill said: "We definitely deserved something from the game. But we conceded one goal from our own throw-in and the other from a corner.
"It doesn't matter how well you play if you make mistakes like that. But the players showed great spirit and could count themselves unfortunate not to get at least a point.
"Both teams deserve credit for putting on that sort of game in the circumstances. Conditions were truly awful.
"We gave ourselves a mountain to climb and there is a repetitious element about the goals we are conceding.
"But we will keep working and I don't want a blame mentality developing because we are all in this together."