A late free-kick from substitute Vicente Rodriguez was enough to give the Seagulls maximum points and take them up to fourth, two points off the play-offs.
He said: "I'm frustrated. The first half was a non-entity in that we cancelled each other out but it was a very good game in the second half.
"We created great chances and could have gone 2-0 or 3-0 ahead. But we didn't take them and that is our Achilles heel.
"Bearing in mind we have two strikers out (Sone Aluko and Matty Fryatt) we've done remarkably well and in the second half we were the better side by far."