Clermont Auvergne landed a crushing blow to Leinster's hopes of defending the Heineken Cup by coming away from the Aviva Stadium with a fine 28-21 victory this afternoon.
Morgan Parra masterminded back-to-back wins for Clermont over the champions, slotting eight of his nine kicks at goal for a 23-point haul.
A crowd of 48,964 - an Irish record for a European pool match - watched Wesley Fofana tear over for a try five minutes before the break to help Clermont push 16-6 clear.
Man of the match Parra managed to convert Fofana's try, adding to three earlier penalties, with Jonathan Sexton booting a brace of penalties for the Irish province.
As Leinster continued to leak penalties, Parra kept Clermont on course to end a run of five straight defeats in Ireland since 2007.
The margin was widened to 25-9 before Leinster recovered to score two tries in the closing quarter-hour through Shane Jennings and Fergus McFadden, the latter's effort coming in a daring last-minute raid.
McFadden's try garnered a losing bonus point for a well-beaten Leinster side, who are now eight points adrift of Pool Five leaders Clermont.
Leinster had only scored one try in their previous three pool games and, with Clermont opening up a five-point lead at the top of the table, a home win was a must.
Eoin Reddan, Heinke van der Merwe, Richardt Strauss and Jennings were promoted to the province's starting line-up following last Sunday's 15-12 defeat in Clermont.
The visitors drafted in prop Raphael Chaume and flanker Julien Bardy, with Australian number 10 Brock James passing a late fitness test.
Hard-hitting Clermont helped themselves to 10 unanswered points closing in on half-time, silencing the home crowd with Fofana's sucker-punch score.
The rugby was typically fast and frantic early on with Leinster seizing on two turnovers and Sexton running smartly to almost link up with Strauss.
Damien Chouly and Napolioni Nalaga carried well before Clermont won a left-sided penalty that Parra poked through the uprights for an eighth-minute lead.
Four minutes later, Leinster lost Strauss to injury as Clermont confidently went about their business with James' pinpoint kicks forcing a couple of spills from Ian Madigan.
Sexton and Parra swapped penalties at the end of the first quarter, the France scrum-half replying almost immediately as Jamie Heaslip came in at the side of a ruck.
The tempo was lifted by the hosts under Sexton's baton, courtesy of a muscular turnover in midfield and pressure from Mike Ross on Chaume in the scrum.
A second three-pointer from Sexton brought Leinster level again, but Clermont were well organised in defence and were quick to counter when offered space.
A loose Madigan kick invited Davit Zirakashvili to hurtle into contact, setting up a power-packed attack that led to Fofana probing in the right corner.
James' tactical kicking was on the money, giving his side plenty of targets and Clermont came to the boil before half-time with Parra's third penalty moving them back ahead.
Sitiveni Sivivatu then sparked a three-man surge down the left. Nalaga was chopped down short of the try-line but Fofana proved unstoppable as he darted onto quick ruck ball to dot down from close range.
Parra's terrific conversion increased the pressure on Leinster, who looked flat at times. Another indiscretion - this time Ross infringed in a scrum - allowed Parra to fire over the first points of the second half, his kick bending in from right to left.
Sexton cancelled that score out as Leinster mounted a strong response, with replacement Cian Healy part of a penalty-winning scrum on halfway. However, Sexton was unable to convert the resulting 50-metre kick.
After the wily Parra took a quick tap, O'Brien's early and dangerous tackle on Sivivatu earned him a yellow card. Leinster's day darkened further as Parra nailed the penalty for 22-9.
Vern Cotter's men had the bit between their teeth now, hammering home their numerical advantage up front. Captain Aurelien Rougerie and Napolioni Nalaga both went close to scoring a try that would have sewn up the result.
Ross was replaced as Leinster's scrum became a liability, and Parra potted a 32-metre penalty having struck the woodwork with an attempt from the right four minutes earlier.
Clermont had a foot on Leinster's throat, but the champions showed their quality as Sexton kicked a penalty to touch, Devin Toner won the close-in lineout at the front and a muscular maul led to flanker Jennings plunging over for a 66th-minute try.
Sexton's conversion closed the gap to nine points. However, the imperious Parra replied by landing his final penalty to punish Healy for not rolling away.
Clermont lost their openside Julien Bardy to the sin-bin for the final five minutes and a late defensive lapse saw Leinster break out of their half through O'Brien and Sexton, with the fly-half delaying his pass neatly for McFadden to score in the right corner.
The conversion was missed and there was no denying Clermont a long-awaited maiden win on Irish soil.