North Dakota State starts a trio of seniors, but a freshman came through in the final minute of overtime as the Bison claimed their first NCAA Tournament win in school history.
Carlin Dupree came off the bench when Taylor Braun, the Summit League Player of the Year, fouled out with 1:18 remaining in the extra session.
Dupree hit a pair of free throws seconds after stepping onto the floor, which gave North Dakota State a lead, then followed that with a tough layup in traffic to help the No. 12 Bison to an 80-75 upset win over fifth-seeded Oklahoma in the second round of the NCAA Tournament.
Lawrence Alexander finished with a career-high 28 points to pace North Dakota State (26-6), while Marshall Bjorkland scored 14 points with six rebounds and Braun tallied 11 points on just 3-of-11 shooting.
Cameron Clarke scored 22 of his 25 points in the second half and overtime in his final game for Oklahoma (23-10) and Isaiah Cousins netted 17 points with eight rebounds.
Jordan Woodard added 13 points and Buddy Hield, a second-team All-Big 12 selection, contributed nine points on 4-of-14 shooting.