No.11 seed Kvitova defeated 2019 Western and Southern winner Madison Keys 7-5 6-4 on a rain-plagued opening day of main-draw play at the tournament outside Cincinnati, Ohio.
The Czech saved eight of nine break points against her serve while breaking Keys three times, and that was enough to pull out the victory.
Kvitova's countrywoman Barbora Krejcikova, the No.9 seed, made her singles debut at the WTA 1000 event with a 6-3 6-2 rout of Daria Kasatkina.
No.15 seed Elise Mertens also was a straight-sets winner, taking down Nadia Podoroska 6-3 6-4, while No.13 seed Jennifer Brady defeated Ekaterina Alexandrova 6-3 7-6 (7-3) in a match that finished shortly before 1:00am local time.
Though only Krejcikova was in action Monday, the field in Cincinnati includes nine of the top 10 players in the rankings, led by Ashleigh Barty and Naomi Osaka in their first appearances since the Tokyo 2020 Olympic Games.
In other matches on the first day of play, Heather Watson defeated Aliaksandra Sasnovich 6-2 3-6 6-1, while Paula Badosa outlasted Petra Martic 4-6 6-4 7-6 (11-9) in a two-hour, 34-minute marathon.
Yulia Putintseva breezed past Zhang Shuai 6-2 6-0, Jelena Ostapenko beat Tamara Zidansek 7-5 6-1 and Jil Teichmann downed Sorana Cirstea 6-2 6-0.
Angelique Kerber beat Maria Sakkari 6-2 6-2, with Alison Riske matching that scoreline in a defeat of Leylah Fernandez.
Shelby Rogers won 6-4 2-1 when her countrywoman Danielle Collins retired with an injury.