The Spudders punched their ticket to the district championship game and also clinced a berth to the state regionals.
Michael Potter scored 19 points, 15 coming in the first three quarters to keep the Spudders close.
Then Sam Landerholf scored nine of his 18 in the fourth quarter as the Spudders pulled away from Onalaska.
Ridgefield will face Kalama in the district finals Saturday at W.F. West High School in Chehalis.