Onalaska senior forward Luke Tepp scored the game-wining goal with 3:50 remaining sending the Hilltoppers to the state semifinal game.
With the score tied at 3-3, Tepp slid in from the corner and beat Kettle Moraine co-op goalie Max LeClaire.
The 4-3 victory is the first win at the WIAA state tournament for the Onalaska boys hockey program since 1995.
Onalaska will face University School of Milwaukee in the state semifinal game Friday evening. Start time is approximately 8:15 p.m.
Joe Witz made 35 saves in goal for the Hilltoppers, improving his record to 19-3-1 on the season. It was the 22nd win of the season for Onalaska.
Also scoring goals for the Hilltoppers were Bryce Bingham, Tyler Ebner, and Ian Earp.