O'Hara scored in each of the first two quarters to help Sacramento State (2-0), ranked seventh in the FCS coaches poll, take a 24-7 lead at halftime.
Northern Iowa (0-3) used Theo Day's 24-yard scoring strike to Logan Wolf and Vance McShane's 4-yard touchdown run to pull within 27-21 after three quarters.
Kyle Sentkowski's third field goal pushed the Hornets' lead to 30-21 and O'Hara capped the scoring on another 3-yard run with 41 seconds remaining.
Jake Dunnniway completed 20 of 33 passes for 199 yards and a touchdown - a 21-yarder to Marshel Martin in the second quarter - for Sac State. Cameron Skattebo rushed for 110 yards on 11 carries and O'Hara carried 19 times for 66 yards.
Day completed 20 of 36 passes for 270 yards with one interception for the Panthers.
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