As stated above, remember you are the expert on the subject. You don't get to do a PhD in something that is already known which automatically makes you the expert in it.
I took my viva 11 years ago now but I remember all of it. I had three "examiners"; although one was my supervisor, so he was more there for moral support, then there was the (university) internal chap,who didn't really ask much and, finally, the external. That was the potental issue for me as a large part of my thesis refutted things that he had published and showed the basic errors in his work. I was a bit worried about that. Not about the quality of my research but about how he would take it. All credit to the man, we got to the relevant section of the thesis, he asked me a couple of questions, sat back in his chair and said - and I really can quote this verbatim, even now - "There is nothing wrong with being proven incorrect by a well made argument supported by good data. Congratulations Chris. That really was a beautiful piece of work." At that point I knew I had it in the bag.
Good luck tomorrow, future-Doctor.
As an aside, one of the best moments in the whole thing for me happened about 2 days after my viva. I went into the university branch of HSBC and asked to speak to an advisor. The woman who I got to talk to was just plain rude and obvious thought of students as lowly scum. I played along until she said "now Mr Smith*...", To which I said, "Actually, that's why I came in. I'd like to change the name on my account to Dr Smith*". Instantly, I went from being scum to proto-deity. It was hysterical. She suddenly couldn't do enough for me. Enjoy that moment.
* Name changed to protect my super-hero identity.