Lopez played a 5 setter on Monday and then played in the doubles. So Surely Andy's got to be fresher. Hope he gets the job done efficiently.
Not sure that Nadal is tired to be honest. He's one of the fittest players on the tour. A 4 setter is nothing for him after only really winning games in straight sets before his match against Del Potro. His injury might be a factor but I doubt it. I think Nadal's tennis will once again be far too aggressive for Murray to cope with provided he gets through.
I say all this because the opposite always happens whenever I predict anything.