Rune has been pretty bad lately with his 7-match losing streak, which, to be fair, was caused by back issues that have been resolved. He snapped his losing streak against Felix Auger-Aliassime but couldn't follow up on the win against Grigor Dimitrov.
It's been a mixed bag for Rune in Beijing as he rated his level at about 20 % of his capabilities, which isn't good but might be good enough for Nakashima, who struggled for much of this year as well. The American loves to play on hard courts, and this one in Shanghai is right up his alley, but will the win over Bernabe Zapata Miralles finally unlock his best? That remains to be seen.
Rune and Nakashima interestingly played at the Next Gen ATP Finals as the American won that match in four sets. Their career went quite differently since then as Nakashima didn't really continue progressing as some had hoped.
Rune did, as he's currently in the Top 10 with a chance to book a spot in the ATP Finals. To get there, he needs to start winning, making this match a must-win.
Rune is the better player overall; there is no point in arguing anything but that, and he's had a far better season even though the form hasn't been that great for either. The condition should be okay for both players, but the win condition is the same.
Nakashima will need to serve well and keep the rallies short because he doesn't have the shot-making ability of Rune. It's the same for Rune, though he has a bigger margin of error due to his superb tennis talent. Both will need the serve, and whoever serves better is closer to winning. I think that would be Rune.
Prediction: Holger Rune to win in two sets.