Radwanska, who will be seeded fourth next week in the U.S. Open, was never challenged. The Polish star won the first five games of the first set and the first four in the second against her Czech opponent, who has been fighting off a cold all week.
The 27-year-old is looking for her second title of the year after winning the Shenzhen Open in China in January.
''It's good that I'm again in this level that I can really play my best tennis, especially before the Grand Slam,'' she said
She will face the Ukraine's Elina Svitolina in the final.
The 21-year-old Svitolina ousted Sweden's Johanna Larsson 6-4, 6-2. Svitolina beat Serena Williams in the Olympics and is ranked No. 23 in the world. She's 4-0 in WTA finals, but this will be her first in a Premier event.
''It feels, of course, more special because it's a premier event,'' Svitolina said. ''For the rest, I don't think this way. It's just a final, you know. My goal is to win a
Grand Slam. It's just another step in the right direction.''
Radwansaka also has never won a Grand Slam, but is looking for her 19th WTA singles title. Fifteen of those have come on hard courts.
She had never made it past the quarterfinals in New Haven, but had a relatively easy trip this year that included a first round bye and straight set wins over Jelena Ostapenko of Latvia and lucky loser Kirsten Flipkins of Belgium
The loss snapped an 11-match winning streak for Kvitova in New Haven, where the Olympic bronze medalist was looking to join Venus Williams and Caroline Wozniacki as four-time winners. She also won the tournament 2012.
The two-time Wimbledon champion said she was fatigued, a bit ill and Radwanska just ran her off the court.
''She's not playing very hard, but she's using her speed, she's putting everything in,'' Kvitova said. ''Even (when) you feel it's winner there, she still can catch it and rallies continue.''
The first match began with three consecutive service breaks before the 21-year-old Svitolina found her touch and took control. The 10th seed broke Larsson at love in the fifth game of the second set and cruised from there.
Svitolina said she's received a lot of congratulations since the Olympics, but she was disappointed because she did not medal and hopes for bigger things next week.
''I wouldn't dream if I didn't think I could achieve this,'' she said of a Grand Slam title. ''I think I need some time to adjust my game to try to compete against top players.''
Radwanska has a bit of an extra incentive on Saturday. A win would give her enough points to clinch the U.S. Open Series bonus challenge and a chance for up to an extra $1 million, depending on her finish at the U.S. Open.
''Definitely it's worth the win,'' she said. ''I will just do everything within my power to win tomorrow.''