Clive Platt's close-range header and Lukas Jutkiewicz's penalty put the Sky Blues two goals to the good and although Jason Scotland grabbed one back, it proved to be a mere consolation.
When asked if his side should have got more from the game, Keane said: "Could have, should have but we still had enough good attacking play, especially in the second half.
"We haven't been scoring enough goals this season, though, and that was the case again. "If you score one at home you've got a chance of getting a point but we gave two very bad goals away.
"We gave ourselves a mountain to climb and weren't quite up to it."