Sioux Center broke a 39-39 tie with 3:11 remaining when Jansen knocked down a three-pointer with 2:22 remaining. BC-IG cut the lead to 42-41 before Sioux Center scored the next four points to put the game away.
Jansen was five-of-10 from the field, making three of five three point attampts. Teammate Becky Kempers added 10 points while Karrisa Davelaar pulled down 11 rebounds.
Kelsey Bolte led BC-IG with a game-high 17 points while Abby Lageschulte added 10.
Sioux Center improves to 25-1 and will face Grundy Center in the Class 2A semifinals Thursday at 2:30 p.m.
BC-IG ends its season at 21-5.
Battle Creek-Ida Grove (21-5) 9 6 14 14 -- 43
Sioux Center (25-1) 8 15 8 16 -- 47