Vinci, seeded sixth, battled Laura Pous-Tio for more than 2 1/2 hours before taking a 4-6, 6-4, 7-6 (7-4) victory.
Hradecka claimed her spot in Saturday's final with a 6-1, 7-5 upset of fifth-seeded Sara Errani. Vinci will be going for her four career title while Hradecka is looking for her first WTA championship. Vinci won their only previous meeting.
Pous-Tio's quarterfinal match Thursday was postponed to Friday because of rain, so she'd played 2 hours, 41 minutes in defeating Polona Hercog 6-7 (7-9), 6-1, 7-5 before taking the court against Vinci.
But Pous-Tio didn't show fatigue and played Vinci in getting to the tiebreaker. Vinci, with Pous-Tio serving, took the first point in the tiebreaker but Pous-Tio came back to win two points. Vinci, however, won the next five points and finished things on her second match point.
For the day, Pous-Tio totaled six sets over 5 hours, 17 minutes covering 429 points. In comparison, Hradecka played 118 points Friday.
Just 35 of those were in the first set when Hradecka established control over Errani, and Hradecka posted three breaks in the second set to advance.
Swim Week Miami Beach 2014 [PHOTOS]