For the first half of an enjoyable encounter it seemed the belief might be trickling back. But goals from Darren Ambrose and Dennis Rommedahl left Portsmouth without a win at home.
Perrin said: "Every game is going to be difficult for us. It is a fight and we have to be ready to fight 90 minutes.
"We have to analyse the games and see where we are losing control. We stopped playing in the second half of this game and have to see why."
After a period of intense pressure, Portsmouth, who had given their opponents a stern examination in the opening stages, took the lead through Dario Silva.
The Uruguayan striker latched on to a long ball from defender Andy O'Brien, calmly firing his first goal for Portsmouth past Stephan Andersen with a fine low shot. It was just reward for some enterprising play from the home side.
Charlton, who have now won all five of their away games this season, initially failed to react in a positive manner.
But manager Alan Curbishley gave his players a roasting in the dressing room, and they came out for the second half transformed.
Curbishley saw it as a test of Charlton's mental strength and on 60 minutes, the answer came. Danny Murphy, anonymous for much of the game, played a smart through ball to midfielder Ambrose, who fired confidently past the Portsmouth goalkeeper Jamie Ashdown.
And it was Murphy who provided the killer blow on 77 minutes, this time setting up Rommedahl, whose powerful shot from inside the penalty area gave Ashdown no chance.Reuse content