The Millers were up 41-29 at the half, but the Spartans came back to win the game 69-63. The win brings the team to a 16-11-0 record on the season (15-11-0 overall in the regular season).
Washburn's boys team clinched second place in the state high school basketball tournament last year.
Richfield will play Blake High School at 7 p.m. Saturday, March 9.
In addition, the Richfield girls basketball team has its final section game against the Chaska High School Hawks at 7 p.m. Thursday at Minnetonka High School.