The Vandals (14-15, 5-10 WAC) clinched a spot in the WAC tournament next week.
Idaho had a 22-point lead with 13:28 remaining when San Jose State's Adrian Oliver woke up. He hit four 3-pointers to spark a comeback that left the Spartans (14-15, 6-9) trailing 78-69 with 1:53 to play.
The Spartans pulled within seven, but ran out of time as Idaho went 6 of 10 from the free throw line in the final 1:30.
Oliver had 24 points for San Jose State.