A double from Glenn Murray earned Palace the points and, although Rovers were denied by the woodwork on a couple of occasions, Berg admitted that they had been disappointing.
"It was neither the performance nor the result we would have liked," he said.
"We had a bad performance and I think we can be much better than this. We played against a good team but we expect to be better than this defensively and offensively. Palace deserved to win, there is no doubt about that.
"Defensively we gave them too much space between our back four and midfield. They had good wingers, we know that, but they were getting way too many crosses.
"I think our full backs handled it quite reasonably but we didn't get as tight as we would have liked, so we have a lot of things to do defensively.
"Going forward we didn't use the ball as we should have done. We should have taken more care with the ball, we were losing it too easily.
"It is a fresh start and I don't know everybody 100 per cent yet. I know those that have played lately better than the other ones.
"It's a good squad we have here but there is room for a lot of improvement and we will do that. I have seen this team play much better than they did today, so hopefully it is a one-off."