Russuvuori bounced back after losing the first set, changing his tactics and overwhelming the German on Saturday (AEDT) to set up a third round meeting with Mikael Ymer.
Zverev may have won last week's Mexican Open and the opening set 6-1 against Ruusuvuori but the tables turned quickly as the Finn produced one of the best displays of his career to date.
The No.83-ranked Finn moved regularly to the net and was aggressive in his approach, leaving Zverev rattled before winning 1-6 6-3 6-1 in a stunning momentum shift.
"I don't even know myself," Ruusuvuori said after the match.
"I wasn't feeling very comfortable in the first set and I was making a lot of unforced errors but slowly in the second I was starting to feel a bit better... Of course, it's one of the biggest wins in my career so it feels good."
He'll next face Ymer, who knocked out No.27 seed Nikoloz Basilashvili.