Deremy Geiger was waiting for this game all season.
Geiger, who played his freshman year at No. 21 Utah State, scored 12 points and grabbed nine rebounds as Idaho beat his old team 64-56 on Wednesday night.
''If I said I didn't have it circled I'd be lying,'' Geiger said of marking the game on his calendar. ''We had a lot to prove tonight.''
The loss broke Utah State's 17-game winning streak, plus their Western Athletic Conference record 25-game league winning streak dating to last season. This was the highest-ranked team Idaho (14-10, 7-5 WAC) has beaten since they defeated No. 16 Iowa in the 1982 NCAA tournament.
The small but enthusiastic crowd stormed the court afterward.
Idaho coach Don Verlin, who spent a decade at Utah State as an assistant to Stew Morrill, beat his mentor for the first time in five attempts.
''What a great win for our program and our players,'' Verlin said, after the Vandals held Utah State to 33 percent shooting, the Aggies' worst performance of the season. Utah State made just 5 of 28 3-pointers.
Jeff Ledbetter led Idaho with 14 points. He made just 3 of 14 shots, but one was a crucial 3-pointer after a scramble for a loose ball that put Idaho ahead 51-42 with 6:45 left. Nine of his points came in a three-minute span late in the second half.
''He didn't have a great shooting night, but when it counted he made a momentum-changer,'' Morrill said of Ledbetter.
Morrill, whose team was seeking to clinch at least a share of a fourth straight WAC title, praised Idaho's defensive effort. He also paid credit to his own team.
''I gave congratulations to my boys for 25 conference wins and 17 in a row,'' Morrill said. ''I knew we were going to lose some time.''
Brockeith Pane scored 14 points to lead Utah State (22-3, 11-1). Their last loss was Dec. 4 at Georgetown.
The game was close throughout, with Idaho up 43-40 with 11:17 left.
Ledbetter hit consecutive 3-pointers to put Idaho up 51-42. Then he was fouled on a 3-point attempt and made all three free throws for a 54-46 Idaho lead.
The game turned into a free throw battle and Utah State was held without a field goal for more than 4 1/2 minutes until Tyler Newbold's 3-pointer cut Idaho's lead to 58-52 with 2 minutes left.
Idaho sank two free throws before Pooh Williams hit a 3-pointer to cut Idaho's lead to 60-55 with 49 seconds left. But the Vandals hung on at the free throw line.
Kyle Barone added 11 points and 12 rebounds for Idaho, which shot 42 percent. The Vandals hit 17 of 23 free throws, while the Aggies made just 7 of 13.
Tai Wesley had 11 points and 10 rebounds for Utah State. Newbold scored 12.
Idaho led 27-24 at halftime, after holding the Aggies to 31 percent shooting, including just 1 of 14 from 3-point range.