The Saints came in with the longest winning streak in the nation, but were stung by a tenacious Purple Eagles defense that forced 16 turnovers and had nine steals.
Kashief Edwards added a career-high 20 points, and Bilal Benn finished with 15 for Niagara (14-13, 7-8 Metro Atlantic Athletic Conference), which lost to Siena in the MAAC championship game last March.
Down by one point with 15 minutes left in the second half, the Purple Eagles pulled away with a 21-3 run that was capped by Demetrius Williamson's 3 with 9:54 to go that made it 70-53.
Former Kentucky guard Ed Davender, the only Wildcat with at least 1,500 points and 400 assists, has died. He was 49.
Guard Naz Mitrou-Long, whose 2015-16 season ended in December due to hip problems, has been granted a hardship waiver for the coming season, Iowa State said.
As the Sooners look to life without superstar Buddy Hield and his sidekicks, it's clear their unseasoned players will need to grow up fast.