Iowa State was generally overlooked as the fifth-best team in the Big 12 Conference this year, but the Cyclones made half their field goal attempts against the Fighting Irish and forced 18 turnovers.
The upset by Iowa State (23-11) created a third-round matchup on Sunday against Ohio State, which rolled over Iona 95-70.
Niang scored 19 points and Melvin Ejim added 17. Together they pushed Iowa State to a 27-point lead with 6 minutes to play after the Cyclones had owned a 12-point advantage at halftime.
The loss by the Irish left trimmed the tournament's eight-team contingent from the Big East down to three before the first weekend of the event. Notre Dame joined Georgetown, Cincinnati, Pittsburgh and Villanova on the sidelines.
Notre Dame (25-10) was led by 14 points from both Jack Cooley and Tom Knight.