Flipkens, who knocked out number one seed Dominika Cibulkova in the first round, continued her impressive run this week with a 7-6 (8/6) 7-6 (7/3) victory over Mona Barthel.
The Belgian was made to work hard for her victory, however, as the third seed battled back from 5-2 down in the second set - saving four match points along the way - to force a tie-break, where Flipkens held her cool to triumph.
She told the WTA Tour's official website: "I can't believe I'm in the finals. I'm excited. I'm going to give 100% and we'll see what happens.
"This week is already perfect - I'm going to enjoy every moment of the final."
Eighth seed Hradecka - who, like Flipkens, has never won a WTA Tour title - finally ended the challenge of French teenage qualifier Kristina Mladenovic with a straight sets victory.
The Czech fired 16 aces on her way to a 7-5 7-6 (7/5) success and she will hope to end an awful record of four defeats from as many matches in WTA finals.
"I was quite young in my first one in Bad Gastein, and I lost a close match, but I told myself not to worry, that I could win my second one," Hradecka said.
"But then I lost that one and two more since, so I hope I can win one finally."