Blackburn are just three points above the relegation zone.
Benni McCarthy had an effort come back off the post.
Allardyce said: “I would say 99 times out of 100 he would have scored but the goalkeeper has got something on it and it has hit the post.
“As hard as we tried after that we couldn’t find another opening. It is one of our problems.
“We changed the system to go more attacking but Crouchy finished us off.
“We are bitterly disappointed with the result and getting no reward after doing a great job on one of the most attack-minded sides in the league.”
