"This was an exciting game because both teams are so evenly matched," UW coach Dean Duerst said. "I'm happy that our team was able to accomplish so much in such a tight game."
The Badgers will remain in South Bend, Ind., for the tournament's second round, where they will face national No. 4 seed Notre Dame (20-1-1) Sunday at noon. The Irish dispatched of Eastern Illinois 4-0 Friday.
The loss to UW was just the second of they year for the Flyers' (20-2) who had won a nation-best 20 consecutive games.
Wisconsin remained a perfect 11-0 in non-conference matches this season and improved to 16-5-1 overall.
Vermeulen, a first-team All-Big Ten selection this year, almost netted UW's regulation goal but Dayton's Jen Simonetti inadvertently converted Vermeulen's free kick for an own-goal, which gave UW a 1-0 lead at 58:05.
Atlantic 10 Offensive Player of the Year Reba Sedlacek was held to just one shot, while Simonetti had none. The latter, though, redeemed herself for the own goal three minutes later when Tesha Kozlowski capitalized on her free kick to tie the match.
Wisconsin sophomore midfielder Kara Kabellis had a game-high six shots, including three (all on goal) in the first half, in helping Wisconsin advance to the second round for the third time in five years.
Each team took 11 shots, and the stalemate continued until sophomore midfielder/forward Allison Preiss set up Vermeulen for her third game-winning goal of the season and team-leading 12th goal of the year overall.