It was only when Dave Kearney went over in the left corner with three minutes left to score the home side’s second try that the result was put beyond doubt. That left eight points in it but a last-gasp penalty from Paulo Buso handed the visitors a losing bonus point.
That is Aironi’s fifth such consolation prize in what has been a dreadfully difficult rookie year in this competition. It could be argued that this latest loss, their 13th, was somewhat unlucky given that they spurned nine kickable points from penalties.
Leinster will point to two such misses of their own in a first-half which was marred by a succession of errors on both sides, both from the boot and the hand, as two scratch sides attempted to find a rhythm.
Much was made of the fact that Leinster were having to make do without 15 of their front-line internationals but the visitors were similarly handicapped minus Azzurri regulars such as Carlo del Fava and Salvatore Perugini.
Still, Leinster were hoarding territory and possession midway through the first-half, which was reached at three points apiece, before one loose pass too many inside the opposition half put them on the back foot and changed the game’s momentum.
Aironi pounced and twice came within inches of crossing the Leinster line before former Munster number eight Nick Williams barrelled through Ian Madigan from the base of a scrum and over the line with Kearney hanging from his waist.
Tito Tebaldi’s conversion made it 10-3 before another loose Leinster pass, this time from scrum-half Paul O’Donoghue, was intercepted by flanker Jaco Erasmus whose sprint for the line was ended within sniffing distance of it by a Niall Morris tackle.
Joe Schmidt must have been fuming and whatever he said at half-time clearly had an effect as Leinster commandeered the lead within seven minutes thanks to a penalty and conversion from Nacewa that sandwiched their opening try from the impressive Morris.
South African prop Richardt Strauss engineered the five-pointer by finding a gap in the Aironi line, handing off a would-be-tackler and off-loading to Morris, an early replacement for the injured debut boy Brendan Macken.
The sight of Shane Jennings and Isaac Boss making their entrances shortly after — bringing to five the number of Irish internationals on the pitch — pointed to a more straightforward closing half an hour but it wasn’t to be.
A long-range drop goal from Aironi full-back Paulo Buso restored parity at 13-13. before a Nacewa penalty again edged the Irish province in front and Kearney made it safe.
I Nacewa; A Conway, B Macken, E O'Malley, D Kearney; I Madigan, P O'Donohoe; H van der Merwe, R Strauss, C Newland; K McLaughlin, D Toner; R Ruddock, D Ryan, S Keogh.
Replacements: N Morris for Macken (14); I Boss for O’Donohoe (48); S Jennings for Keogh (48); S Shawe for Newland (67); I McKinley for Madigan (70); J Harris-Wright for Strauss (79); J McGrath for van der Merwe (79).
P Buso; K Robertson, G Pizarro, H San Martin, D Demas; J Marshall, T Tebaldi; Alberto De Marchi, R Santamaria, F Staibano; M Bortolami, J Furno; N Cattina, J Erasmus, N Williams.
Replacements: L Ferraro for Santamaria (62); Andrea De Marchi for Alberto De Marchi (64); L Redolfino for Stabaino (68); GF Biagi for Furno (68); A Benatti for Erasmus (68); P Travagli for Tebaldi (68); M Pratichetti for Pizarro (70).
Referee: N Owens (WRU).