For Aironi, Naas Olivier knocked over 11 points to add to Nick Williams' first-half try as the Italians picked up a defensive bonus point, their first of the new season.
After Humphreys and Olivier had missed a penalty apiece, Whitten gave Ulster the lead with the first try of the game on 17 minutes.
Humphreys missed the conversion and three minutes later Olivier inched the home side back into it with a penalty.
But Ulster responded immediately when second row Dan Tuohy went over, Humphreys' conversion making the score 12-3.
With ten minutes remaining in the opening half former Munster and Auckland Blues No. 8 Williams grabbed Aironi's first try of the season, and Olivier's conversion got them back to within two points.
Olivier put the Italian side in front with another penalty before Humphreys gave Ulster the lead again with a penalty on the stroke of half-time, Brian McLaughlin's side leading 16-15 at the break.
The South African stand-off put Aironi back in front five minutes after half-time before young flyer Craig Gilroy crossed for Ulster's third try, again converted by Humphreys to make it 22-16.
Humphreys added another penalty ten minutes from time to put Ulster two scores clear.
Prop Jerry Cronin was then sin-binned with five minutes to go and Olivier got Aironi back to within six points but Ulster held on for a narrow victory.
|Aironi Rugby Score Card|
|Ulster Rugby Score Card|