Aironi (6) 15
Pens: Mercier (4) Drop: Mercier
Ulster (9) 22
Try: Diack Con: O'Connor Pens: O'Connor (5)
Ulster's Adam D'Arcy in possession against Giulio Toniolatti of Aironi
Ulster made it two wins from two in the Magners League thanks to a hard-earned success over Aironi in Viadana.
Number eight Robbie Diack got the only try of the game by intercepting Ludovic Mercier's pass and running on for a 60th-minute touchdown.
Fly-half Mercier landed four penalties and a drop goal for the Italian club while Niall O'Connor kicked Ulster's other 17 points.
Ulster are now second in the table, one point behind Munster.
League new boys Aironi briefly had their noses in front early in each half but the Irish province just about deserved their victory.
Ulster tight-head prop Declan Fitzpatrick limped off early in the game and was replaced by Bryan Young.
Mercier kicked Aironi into an eighth-minute lead when Ulster were penalised for coming in at the side but two kicks by O'Connor put the visitors 6-3 up.
The fly-halves exchanged further penalties to leave Ulster 9-6 up at the break.
Frenchman Mercier landed a drop goal and a 54th-minute penalty to put Aironi into the lead for the second time.
Then came the crucial try as Diack stretched to intercept and charge for the line.
Mercier cut Aironi's deficit to four with another penalty but O'Connor replied.
With Pedrie Wannenburg sin-binned for not rolling away, Ulster came under pressure at the end but kept the home side at bay.
Aironi did get over the Ulster line but the video judge ruled they had not got the ball down.
Aironi: Laharrague, Toniolatti, Quartaroli, des Fountain, Rubini, Mercier, Tebaldi, A. De Marchi, Ongaro, Perugini, Del Fava, Geldenhuys, Erasmus, Krause, Williams.
Replacements: Pizarro for des Fountain (2), Canavosio for Tebaldi (45), Redolfini for A. De Marchi (60), Ferraro for Ongaro (60), Bortolami for Del Fava (45), Sole for Erasmus (60).
Not used: A De Marchi, Benatti.
Ulster: D'Arcy, Seymour, Cave, Wallace, McIlwaine, O'Connor, Marshall, Court, Brady, Fitzpatrick, Muller, Barker, Wannenburg, Henry, Diack.
Replacements: Porter for Marshall (60), McAllister for Court (73), Kyriacou for Brady (69), Young for Fitzpatrick (4), Caldwell for Barker (62), Faloon for Henry (60).
Not used: Whitten, Smith.
Ref: David Jones (Wales).