Benetton stunned error-strewn Leinster as they made history by winning for the first time in Dublin, triumphing at the RDS in the Guinness PRO14.
Second-half tries from Federico Ruzza and man of the match Tommaso Allan, adding to Luca Bigi's early maul effort, ensured it was a famous night for the Italians who set a new club record for wins in a championship season with their 11th success.
Barry Daly's 11th try of the campaign on the stroke of half-time had Leinster leading 12-5, but they only mustered a single penalty from Joey Carbery in the second half as they fell to only their second defeat in 38 home games stretching back to December 2015.
With Scarlets, their Champions Cup semi-final opponents next weekend, also losing on Saturday in Edinburgh, Leo Cullen's men are still set to finish top of Conference B and have a home semi-final.
They are five points clear, have more wins and a much greater scoring difference.
Hookers Richardt Strauss and Bigi swapped early tries, the former breaking off a well-set Leinster maul for a sixth-minute opener.
The Treviso side replied within four minutes, a strong drive powering Bigi over near the right corner.
Carbery's conversion was the difference between the sides for much of a rather listless first half.
Leinster's attack was too predictable at times, and a dangerous kick from Jayden Hayward almost created a try for Monty Ioane at the other end.
Jordan Larmour was fizzing with intent, breaking on the right from a Carbery-inspired move. Benetton's well-organised defence held out until Leinster took a scrum following successive penalties late on, and Carbery and Larmour passed to the left for Daly to ground the ball under Andrea Bronzini's nose.
Sean O'Brien was replaced at half-time and was touching his shoulder on several occasions during the opening half.
Leinster carried the early second-half threat as they looked to build a match-winning position from 12-5, but Benetton made it a two-point game again when Tito Tebaldi's awkwardly bouncing kick was gathered by Jayden Hayward ahead of Fergus McFadden, and the full-back passed inside for blindside Ruzza to cross to the left of the posts.
Italy international Allan missed with a poor conversion attempt before redeeming himself with an opportunist 53rd-minute try. Leinster captain Jack McGrath's loose pass was hacked on by Allan who dribbled past the try-line to score and convert. Suddenly, Benetton's first victory in 18 visits to the Irish capital looked a real possibility.
Carbery snapped back three points from the tee, closing the gap to 17-15, but the final quarter was scoreless. Leinster lacked the necessary composure and territory to take advantage of scrum-half Tebaldi's sin-binning for illegal use of the boot at a ruck.
Handling errors blighted the hosts' attempts to build momentum up to and past halfway, and with Nasi Manu, Marco Fuser and Cherif Traore prominent in an ultra-physical pack, Benetton stood firm to draw back within a point of fourth-placed Ulster in the race for the Champions Cup play-off spot.