The summer signing levelled matters when on loan Palace goalkeeper Stuart Taylor raced from his line to see Carlisle out-jump him to head home.
Carlisle was Rangers' most dangerous player on the afternoon, but squandered a number of chances to beat Taylor during the game.
The home side went in front on the stroke of half time, when Forssell saw his venomous shot parried by Lee Harper, but only as far as Clinton Morrison, who laid the ball back, via Jamie Pollock, for Simon Rodger.
Rodger struck the ball goalbound, but it struck Forssell and looped past the wrongfooted Harper and into the Rangers net.
That came at the end of an eventful half, which had seen Taylor have to make an impressive treble save, including a block at point blank range from Paul Furlong.
Forssell and Fan Zhiyi both had chances at the other end before Carlisle came close with his first effort of the afternoon, heading just wide.
The pendulum then swung the way of Palace as half time approached, with Forssell (twice) and Morrison having chances before the opener came after the former Chelsea striker saw a well-struck volley palmed out.
The second period was a more restrained affair, with Palace captain Neil Ruddock heading wide early on before midfielder Jamie Pollock was stretchered off with concussion after a collision with Ian Baraclough.
Morrison had another chance before the ever-dangerous Carlisle levelled matters when Taylor went walkabout.
Forssell had the best chance of a winner as both teams tired in the latter stages, but the Finnish star blazed his shot over the bar from little more than ten yards.
