I predicted this.....Nadal kept the ball nice and deep (and high) to begin with and was up a break.....but then fell into his natural tendency of using the angles, and that played right into Zverev's hands....
Zverev can only win if Nadal drops the ball short, and especially near the tramlines to give Zverev space to swing.
If Nadal keeps the ball deep, then there is nothing Zverev can do.
Nadal does not even need to play aggressively, he just has to keep the ball deep (don't need to hit the ball hard or flat).
Nadal leads 5-2, but Zverev won easily on Indoor Hardcourt, and most of Nadal's wins were close because Nadal's natural tendency to use the tramlines played into Zverev's hands.