Nadal is pretty good at creating the intimidating factor by jumping up and down from the get go like a buffoon (that's for you herc darling). This being the very first round doesn't really work in Ryan's favour. He's a bit of a headcase so he needs time to feel confident. A 2nd round meeting would have been ideal for him.
First set will have to go. A 5 setter format though works in his favour since he seems to take time to come together. Nadal doesn't have too many weapons. Harrison just needs to break Nadal's forehand down somehow or keep him away from it.