Fish, the top seed, needed just 77 minutes to trounce France's Jeremy Chardy, the seventh seed, 6-4, 6-1.
"I thought I played one of the better matches of the year for sure and that kid could play, there's no doubt about that," said Fish, who has not dropped a set at this tournament.
Korolev advanced to his first ever final on the men's tennis tour by beating Belgium's Christophe Rochus 6-1, 7-5.
"I am very happy to reach my first ATP World Tour final, finally," said Korolev.
Fish, 27, and Korolev, 21, have never faced each other.
Sunday's winner will pocket a $79,000 first prize.