Spieth told reporters: "I've never had a round where I've been nervous on every single swing, shot, and putt.
"I'm sure that will happen [on Sunday], but hopefully I can channel it positively and stay grounded, stay cool, and see what happens.
"I'm in a great position, a position I haven't been in before but I'm excited about it. This is a place I've always dreamed about. It's kind of heaven on Earth for me."
Spieth is the second-youngest Major leader after 54 holes since 1945.