The top-seeded Lady cats opened up a big halftime lead and went on to post a 57-22 victory over the eighth-seeded Lady Jays.
Koshkonong took an early 5-4 lead, thanks to a 3-ball from Sydney Wade, but after that, it was all Thayer.
Samantha Oakes (14 points) racked up six points in the first period and Thayer closed the frame on a 13-2 burst to grab a 17-7 advantage after one.
Koshkonong had trouble finding an offensive flow in the second period and the Lady Blue Jays scored just three points -- on a hoop from Chelsy Carey (six points) and free throw by Sam Collins (seven points) -- in the stanza.
Thayer, however, had little problems at putting the ball in the basket and paced by Whitney Mills' seven points in the second, the Lady Bobcats took a 34-10 lead to intermission. Mills led all scorers with a game-high 17 points.
Thayer opened the third with six unanswered points and when the third period ended, the Lady Cats enjoyed a 48-18 lead.
Kelsey Steed logged seven points for Thayer, while Emily Eckman, Lacey Hawkins and Laken Martin finished with five points apiece.
Courtney Hargrove had two, while Miranda Webber and Macee Smith scored one point each.
Taylor York recorded three points for Kosh, with Elizabeth Sanders posting two points and Desaray Collins one point for the Lady Blue Jays.