For myself, the key in performance is to concentrate on the music, e.g., creating subtle, unmarked crescendoes and decrescendoes when appropriate (something Pablo Casals suggested once in an interview, yes, I know, a cellist), shaping phrases, pedaling, and getting to know the quirks of whatever strange piano you're playing (a little Strange can be fun). The key is to occupy one's mind with all that, so that letting yourself wander down the negative, paranoid path of worrying about memory vanishes.
The enemy of performance, of course, is being forced to play when you are not yet fully prepared.
The joy of performance is achieving that Zen state where you are totally in the here and now, ignoring past errors, focused on the moment or a measure ahead.
One of the benefits of aging is that as one gives more and more concerts one finds performing just a bit easier with each one.