The Lancers built a 23-16 halftime lead, but the Broncos rallied for a 39-point second half in a non-conference contest played at Racine Prairie.
Katie Matrise led St. Joseph with 26 points, as she knocked down five 3-pointers and was 7-of-8 from the free-throw line.
Alexis Mattox added 10 points for the Lancers.
"Our girls came out from the start and played well on both ends, as we built up a 13-point lead in the first half," Jason Coker said. "The second half, unfortunately, was filled with turnovers, which swung the momentum the other way."