Only ten seconds remained when Umeå went to a last attack at a disadvantage 63-64.
Import Janee Thompson tried to create a surface and pulled off a three-point attempt.
The Södertälje players held their breath and could see the finish bouncing outside the basket.
But maybe the home team breathed a sigh of relief and became too ball-watching.
Södertälje got one last finish
Because instead of getting the ball and saving further play, the return went straight down to the right-wing German-American Ama Degbeon who scored two points, with only two seconds left.
Södertälje, who also had the lead with six points twice in the match, had one last attempt to take over the lead but that end was never close and Västerbottningar could celebrate the advancement.
For Umeå's part, rival Luleå is now waiting in the semifinals.