They began like world beaters and looking like notching up a bonus point by half-time. But they allowed Aironi, yet to win a Magners League game all season, back in the game and they could have run the hosts even closer.
In the end there was no bonus for Ulster despite early tries from Tom Court and Craig Gilroy, with Declan Fitzpatrick getting a third late in the game.
It took just three minutes for Ulster to get going. A long touchfinder from Pienaar, a catch and take in the lineout and Court drove over the line. A second try came five minutes later when Gilroy ran a seventh try in seven starts.
Pienaar converted and added a penalty soon after as the Italians struggled to get out of their own half.
Then Ulster lost concentration with discipline dropping and Aironi’s first visit to the red zone allowed Riccardo Bocchino to pop over a penalty on the half hour.
Aironi cut the leeway further two minutes from the break when a series of rucks allowed the ball to be spread wide on the right for full-back James Marshall to burst through weak tackling to run under the posts for Bocchino to convert.
Aironi were a changed team in the second half. They were buoyed by Ulster ineptitude, who lost captain Johann Muller to the sin-bin after collapsing a maul.
Coach Brian McLaughlin shifted his bench into action and it brought dividends. Pienaar, moved to scrum-half, floated over a second penalty on 62 minutes.
Though Ulster’s play was still full of errors, they did manage a third try in the 73rd minute with replacement prop Fitzpatrick driving over from a ruck to end the scoring.
Scorers for Ulster: T Court, C Gilroy, Fitzpatrick try each; R Pienaar con, 2 pens.
Scorers for Aironi: J Marshall try; R Bocchino con, pen.
ULSTER: A D’Arcy (Danielli, 47); A Trimble, N Spence, P Wallace, C Gilroy; R Pienaar, P Marshall (L Marshall, 58); P McAllister (Fitzpatrick, 47; Cronin, 75), N Brady (Kyriacou, 47), T Court, J Muller, capt, T Barker (McComb, 65), C Henry, P Wannenburg, W Faloon (Diack, 75).
AIRONI: J Marshall; K Robertson, G Pavan (Pizarro, 64), M Pratichetti, D Demas; R Bocchino (Rubini, 70) P Travagli (Tebalti, 65); A De Marchi, R Santamaria (D’Apice, 70), U Gamboa, J Furno (Biagi, 66), M Bortolami, capt, J Sole, G Krause, N Williams.
Referee: Leighton Hodges (WRU).