Sean Russell gave OSA FC the lead 1-0 in the 55th minute when he headed home a goal that began with a free kick.
12 minutes later the Spartans were level at 1-1 when Matt Dwyer scored. OSA FC needed just a tie to clinch the playoffs, but instead they got a winner in the late stages.
Gabe Kellum scored in the 88th minute to give the Seattle-area club a 2-1 win and the NW Conference title.
OSA FC now advances to the NPSL playoffs July 9 where they will be seeded with 3 clubs from the Golden Gate Conference and match-ups will be determined by total regular season points.