Leinster needed a last-minute drop-goal from Jonathan Sexton to edge Treviso 19-18 at Stadio di Monigo on Saturday.
Treviso, who have beaten the reigning PRO12 champions the Ospreys and put up a good fight against Munster already this season, started brightly and they had the better of the Heineken Cup holders in the first half.
After Alberto di Bernardo had kicked them into an early lead, a yellow card for Leinster flanker Kevin McLaughlin gave them a one-man advantage and they duly capitalised as Robert Barbieri powered his way over from a quickly taken penalty.
The conversion was missed and the Irishmen held on until they were restored to their full complement, after which Sexton managed to slot over a penalty to reduce their arrears slightly but they went into the half-time interval 8-3 behind.
Leinster came out firing at the start of the second half though and the talismanic figure of Brian O'Driscoll showed that he still has plenty left in the tank ahead of the Lions' tour to Australia next summer as he crossed to level the scores.
Sexton kicked the conversion and added a penalty about 10 minutes later to open up a five-point lead for his side but the Italians refused to let the opposition get away and replacement Kris Burton pegged them back with three points.
Sexton restored the five-point lead with around five minutes left to play but the men from Dublin were left stunned when replacement scrum-half Fabio Semenzato crossed moments later and Burton knocked over the conversion to put the hosts in the lead.
With time ticking away it looked like Treviso were going to be able to boast a win against both of last season's PRO12 finalists but they were left heartbroken as Sexton stepped up to slot over a last-minute drop-goal for Leinster.
Treviso will be encouraged once again by their performance but the losing point will feel like scant consolation after coming so close to victory.
Leinster, meanwhile, will be delighted to have snatched the win after another patchy early-season performance.
Tries: Barbieri, Semenzato
Pens: di Bernardo, Burton
Pens: Sexton 3
Yellow card: McLaughlin (Leinster - 17th min)
Treviso: 15 Luke McLean, 14 Edoardo Gori, 13 Tommaso Benvenuti, 12 Alberto Sgarbi, 11 Ludovico Nitoglia, 10 Alberto Di Bernardo, 9 Tobias Botes, 8 Robert Barbieri, 7 Alessandro Zanni, 6 Simone Favaro, 5 Corniel Van Zyl (c), 4 Francesco Minto, 3 Ignacio Fernandez-Rouyet, 2 Leonardo Ghiraldini, 1 Alberto De Marchi.
Replacements: 16 Franco Sbaraglini, 17 Michele Rizzo, 18 Lorenzo Cittadini, 19 Valerio BernabÃ², 20 Dean Budd, 21 Marco Filippucci, 22 Fabio Semenzato, 23 Kristopher Burton.
Leinster: 15 Ian Madigan, 14 Andrew Conway, 13 Brian O'Driscoll, 12 Fergus McFadden, 11 Fionn Carr, 10 Jonathan Sexton, 9 Eoin Reddan, 8 Jamie Heaslip (c), 7 Shane Jennings, 6 Kevin McLaughlin, 5 Devin Toner, 4 Damian Browne, 3 Mike Ross, 2 Richardt Strauss, 1 Heinke van der Merwe.
Replacements: 16 Sean Cronin, 17 Cian Healy, 18 Jamie Hagan, 19 Leo Cullen, 20 Jordi Murphy, 21 John Cooney, 22 Noel Reid, 23 Isa Nacewa.
Venue: Stadio di Monigo
Referee: Ian Davies (Wales)
Assistant referees: Carlo Damasco (Italy), Stefano Traversi (Italy)
Television match official: Stefano Marrama (Italy)
Timekeeper: Walter Borghetto (Italy)
Assessor: Giannino Cappellozza (Italy)