Haase, of the Netherlands, upended top-seeded Jo-Wilfried Tsonga 7-5, 7-6 (7-4) in one of the day's semifinals, gaining his fourth career final and second this year.
It was his third upset of the week after previously taking out No. 7 Vasek Pospisil and No. 3 Fabio Fognini.
Tsonga, meanwhile, saw his chances to grab one of the four remaining spots for the season-ending ATP World Tour Final take a hit with his second straight semifinal loss.
In Saturday's other match, Germany's 35-year-old Haas rallied for a 3-6, 6-4, 7-6 (7-0) victory over Lukas Rosol.
The 2001 Vienna winner will be going for his 15th career ATP Tour title. He took an April victory in Munich after falling at the San Jose final in February.