Benetton Treviso 29 Leinster 13
Luke McLean and Brendan Williams claimed the second-half tries that earned Magners League new boys Benetton Treviso victory over Leinster at the Stadio Comunale di Monigo tonight.
McLean's try put Treviso in command and a breakaway try from Williams at the death wrapped up victory.
Tobias Botes converted both tries and landed three penalties while Kris Burton weighed in with two drop goals.
Isa Nacewa claimed all Leinster's points with a converted first-half try and two penalties.
Leinster raced into an early lead through Nacewa's try which he improved for a 7-0 lead.
Treviso responded with two Botes penalties and two Burton dropped goals while Nacewa landed a penalty to leave the home side 12-10 ahead at the interval.
Nacewa's second penalty edged Leinster ahead early in the second half.
But another Botes penalty and McLean's try, converted by Botes, gave Treviso some breathing space.
McLean made the most of some weak Leinster tackling for his score which gave the home side the initiative.
Leinster did enjoy some concerted pressure towards the end but Nacewa and Fergus McFadden were both guilty of missing penalties.
This was Leinster's second defeat in three matches which represents a disappointing start to the season under new coach Joe Schmidt.
Although Leinster were without Ireland star Brian O'Driscoll they did have Ireland trio Gordon D'Arcy, Rob Kearney and Eoin Reddan making their first starts of the season.
Treviso had Maori winger Joe Maddock making his debut after his summer move from Bath.