Landon Tatum added 10 points, and Djim Bandoumel and Kyle Barone had nine rebounds each for the Vandals (18-12, 9-5 Western Athletic), who have won seven of their last eight games and are the No. 3 seed in next week's conference tournament in Las Vegas.
Idaho faces sixth-seeded Hawaii in a first-round game on Thursday.
James Kinney had 19 points and made five 3-pointers for the Spartans (9-21, 1-13), who are the No. 8 seed and play top-seeded Nevada in the first round. Keith Shamburger added 14 points and Wil Carter 12.
San Jose State trailed 54-50 with 3:54 remaining, but Idaho closed out the game by scoring all its points with free throws.
The Vandals made 16 of 22 from the line down the stretch.
- San Jose State