Idaho State (10-16, 7-10 Big Sky) used a 6-0 run to tie the game at 65 with 23 seconds remaining. Northern Arizona's Max Jacobsen missed the front end of a 1-and-1 but Idaho State couldn't convert, leaving the Lumberjacks with possession in the waning seconds.
Yanku was fouled with 6.1 seconds remaining, and hit 1 of 2 at the line as Northern Arizona (12-16, 9-8) snapped a three-game losing streak.
Yanku also had the winning basket in a 67-65 win against Idaho State earlier this season.
Upshur hit a career-high eight 3-pointers. Jacobsen added 20 points and eight rebounds for the Lumberjacks.