Sascha Zverev showed a lot of patience in his 2nd round victory over Nakashima especially with his 2nd serve which at times failed him massively. As opposed to his 2nd serve, his 1st serve funcitioned great throughout the match as he won over 80 % of his 1st serve points. Speaking of his serve Zverev said:

"Take the 10 double faults away and it's perfect, and I wasn't broken today."

His 2nd serve woes were particularly bad in the 2nd set but even so he managed to hang on to force the tiebreak. In it, however it was the American who managed to take advantage of the 2nd serve woes and win it. On that Zverev said:

"Obviously I didn't want to lose the second set, but I know that if I play my game I can still win- So it was one set all, everything was still open. He's a good player [and] has an incredible backhand... He's a great player, I think, with great potential."

Zverev praised Nakashima greatly and while the American showed fighting spirit it didn't help him much in the next two sets as Zverev completely took control. His 2nd serve got better and that was too much for Nakashima to handle.

After the match he did praise Nakashima even more. Speaking about his serve he said:

"His serve surprised me a lot, because he doesn't serve very fast. But his placement is incredible. He can go any corner. He has all the serves that you need. His second serve is incredibly good."

Even so it was the serving of Zverev which won him the match and the American surely observed and learned something from it.

https://twitter.com/usopen/status/1301268508869787649