Siakam added nine rebounds for the Jaguars (9-15, 3-9 Summit League), who ended a seven-game losing streak.
Sean Esposito sank four 3-pointers among his 18 points, Ian Chiles scored 15 and Alex Young had 14, reaching double digits for the 14th straight game.
Travis Bader hit six 3-pointers and scored 20 points to pace the Golden Grizzlies (12-13, 6-7). Reggie Hamilton added 18 points and Laval Lucas-Perry 11. Drew Valentine grabbed 12 rebounds.
Trailing 59-57, IUPUI went on a game-turning 7-0 run to take a 64-59 lead with 7:43 to go. Oakland got within one point four times after that, the last at 76-75 with 33 seconds left, but Young made a free throw and Esposito two to close it out.
The teams split the season series.