Pervak defeated Urszula Radwanska 6-2, 6-4, while Birnerova trailed 3-6, 5-3 when defending champion Alla Kudryavtseva retired with a strained left thigh muscle in the second set. The 27-year-old Birnerova, who mostly plays on the ITF circuit, was playing in her first career WTA tour semifinal.
The 52nd-ranked Pervak is looking for her first career title and has not dropped a set on the way to her second final of the season.
The Russian won five consecutive games in the first set and another five straight in the second to rally from 4-1 down.
The sixth-seeded Kudryavtseva strained her left thigh while running to the net to return a drop shot. She received medical treatment before returning to the court, but had to quit after losing her serve in the next game.
Pervak is enjoying her best season, reaching the fourth round at Wimbledon and her first WTA Tour final in Baku in July.