A reason to believe in it?

Nakashima is down 5–0 against Zverev, you really have to dig deep to find arguments in his favor.

Nakashima has only won 2 sets against Zverev while losing 13; the tally is harsh but quite logical. Nakashima doesn't excel at returning serves, and Zverev is one of the best servers in the world; that alone makes it difficult for the American to do anything. Furthermore, Zverev is even more patient and solid in the game; he's more consistent on his backhand and simply does many things a little better—it's in the details that things are decided. Even though Nakashima has been improving his level and consistency for the past few months, he's still "stuck" against the best players. The matchup against Zverev is incredibly tough for him, poor guy. Yet, I quite liked his first-round performance; you can't ask him to do more, but that was against Carabelli, and it's easier to play your own game against him.

Zverev also had an excellent first round against Berrettini. The German was locked in, allowing him to get back into the game and dominate him while maintaining his attacking intent—a fundamental skill he tries to incorporate into every match. He won 14 out of 16 points at the net! He's maintaining an incredible serve and has somewhat eliminated his passivity. His start to the year has been quite solid, I think. There are still a few slip-ups, like against Kecmanovic last week, but Kecmanovic's level in that match was something else. The Serb played one of the best matches of his life and had already given Zverev a hard time. Nakashima is nowhere near that level, so he would need tremendous tennis plus a tactical adjustment, and I don't believe that's possible.