The Nadal vs Zverev match will be interesting, but I think it will end up 2:0 in favor of Nadal. Rafa so far has the easiest route and this is the first time that we will be tested. And he hasn't lost a set in those match, so I reckon it will be the same against Zverev, who somewhat has to dig dipper in the 2nd set as he was force to a tie-break.
I don't think that Zverev can win a set against nadal. Zverev also has not lost a set yet in this tournament but that is not so special to me because both of them only played 2 matches so far . If zverev has a good day than he can beat everyone but nadal on clay is something different to me. If he reaches a good form or even only a average form then there is not much that other players can do against it on clay. He is already 34 years old so maybe the gap between him and the other players is already getting closer but as of now he is still ahead of them.
We are completely wrong in our prediction, on the contrary, Zverev won 2:0 against the best court player in Nadal. I don't think that Nadal is losing step, it's that that Zverev really played a perfect game today.
So it's Thiem vs Zverev, I still leaning on Thiem to win here, next to Nadal, I would say that he is the next best player. So let's see if Zverev can continue his winning or Thiem will stop him here. 2:1 for me - Thiem.