Portsmouth sunk to the bottom of the League One table despite collecting their second draw in five days.
Jon-Paul McGovern almost put Carlisle ahead when his 25-yard free-kick hit the post and keeper Simon Eastwood, who just stopped it rolling into the net.
Eastwood then denied Liam Noble before Rory Loy rounded him to put United ahead after Lee Miller's pinpoint pass.
Liam Walker earned Pompey a point with a penalty after keeper Mark Gillespie brought down substitute John Akinde.
VIEW FROM THE DRESSING ROOM
Portsmouth caretaker manager Guy Whittingham told BBC Radio Solent:
"On the balance of things it was probably a fair result.
"It's probably one a few weeks ago we might have lost and heads might have gone down after going a goal down but it shows there is a spirit building there.
"We haven't scored enough of the penalties we've been given this season, but Liam took it well and I'm delighted for him because it's not been easy for him. He has been in and out the side and all he wants is to get a run in the side, so to come up with the courage to take that penalty was great.
"The important thing is we're making sure the players give everything they have and we're making sure that we're defensively a lot harder to break down."
Carlisle boss Greg Abbott told BBC Radio Cumbria:
"I know it's not been a tough place to come, but their players are playing for these fans and you're always up against it. I thought the boys were really competitive, the attitude of their play was excellent.
"Sometimes it's a sob story for Portsmouth and they're playing in emotion country at the moment and I think that's probably what got them the point.
"They'll think they deserved it and we're a bit aggrieved we haven't got three but I'm not complaining too much."