The former Newcastle United goalkeeper produced a superb display as Neil Lennon's side avenged the defeat suffered in the reverse fixture a fortnight ago.
Forster told BBC Sport: "It's tremendous. Words can't describe it. We put in so much effort away and couldn't see it through, but today we have and we're delighted. We have a fantastic squad; whoever comes in can do the job.
"Even with injuries everyone was tremendous and played their part. We deserved it in the end.
"We defended really well. We had a good look at them a couple weeks ago and knew what we wanted to do. We didn't do much wrong in the Nou Camp, but we did it all today."
Lennon has claimed that the win came on one of the "proudest nights" in his career.