O'Brien, a transfer from Maryland, completed 19-of-23 passes for 219 yards as Wisconsin (1-0) survived a scare in its 2012 opener as the Panthers amassed 21 second-half points.
The Badgers' Montee Ball racked up 120 yards on 32 carries and scored a touchdown for the 21st straight game.
Freshman quarterback Sawyer Kollmorgen threw for 265 yards, going 18-for-34 with three touchdowns for Northern Iowa (0-1).
The Panthers' David Johnson gained 107 yards and and caught two TD passes.
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