He made one-handed saves from Joey Barton and substitute Peter Lovenkrands and with just two minutes remaining, blocked Carroll's goalbound effort with his foot as wave after wave of black and white attacks were repelled.
Newcastle's misery was complete when, with just seconds remaining, Adam fed Campbell and he beat Harper with a perfectly-placed shot into the far corner.
Harper said: "Their goalkeeper had one of those special days that can happen every now and again, but it is a disappointed dressing room in there.
"Goals changes games in the Premier League and when a team comes here, you don't want to give them anything to hang on to and that's what we did.
"We gave them a penalty and they managed to hang on to that, and they caught us with a sucker punch at the end when we had to go chasing the game, so it was a disappointing day."