The person capable of most effectively sabotaging a performance is the performer himself or herself. We tend to associate a critic with destructive comment, and our inner critic tends to reflect the usual cultural meaning of criticism as negative. A critic can be a good friend, and a necessary part of the creative process. The first thing to do is to educate the inner critic to make some positive statements. To say what it wants and not what it does not want.
Criticism is useless if it gives no indication of how to improve.
Think about what you want to do rather than what you want to avoid. Use feedback from the critic to construct internal movies of what you want to happen. Hear how you want the piece to sound. See and hear yourself performing as you wish to before associating into the picture. Give your critic an appearance and a name.