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.
Tomas Sanchez led the Bengals with 17 points. Andre Hatchett scored 13 and Chris Hansen had 12. Jeffrey Solarin added 11 points and 11 rebounds.