Clermont Auvergne threw Pool 2 of the Heineken Cup wide open with a thrilling 20-13 victory over Leinster at Stade Marcel Michelin.
A losing bonus point keeps the Irish top of the group on 10 points but their French counterparts are just one behind with Racing Metro on eight.
Shane Horgan and Julien Malzieu exchanged early scores while Johnny Sexton and Morgan Parra had two penalties apiece, but the game was won in the third quarter when Clermont full-back Anthony Floch crossed for the decisive score.
The visitors stunned Clermont with a well-worked try after only four minutes, Sexton and Gordon D'Arcy involved before a Shane Jennigs pass was partially intercepted by Malzieu, only for Horgan to recover the ball and bundle over.
Sexton added a difficult conversion but the lead lasted barely two minutes as the French champions hit back immediately, Brock James denied a try by some desperate defending before Aurelian Rougerie fed Malzieu, who broke through Sexton tackle to score.
Parra tied the score and the frenetic start continued with Leinster immediately working their way back into the opposing 22.
Their willingness to run the ball at every opportunity was rewarded with a penalty on the left and Sexton struck it over to put them 10-7 in front on 13 minutes.
The odds looked stacked against the visitors as the half wore on though with inspirational number eight Jamie Heaslip and flanker Sean O'Brien both feeling the effects of some huge hits.
Parra kicked Clermont level after 25 minutes and Leinster were let off the hook when full-back Floch shot an easy drop goal attempt wide, shortly before the sides went in at the break tied at 10-10.
Heaslip was finally forced off shortly after the restart and it was not long before Clermont hit the front for the first time.
After a sustained spell of pressure, Floch sidestepped D'Arcy's tackle to find the corner. Parra converted to give Clermont a 17-10 lead.
The sides then traded penalties around the hour mark as Leinster stood firm before Parra missed a penalty with six minutes left that could yet cost his side dearly in the final analysis.
Tries: Floch, Malzieu
Cons: Parra 2
Pens: Parra 2
Pens: Sexton 2
Clermont: 15 Anthony Floch, 14 Napolioni Nalaga, 13 AurÃ©lien Rougerie, 12 Gavin Williams, 11 Julien Malzieu, 10 Brock James, 9 Morgan Parra, 8 Sione Lauaki, 7 Alexandre Lapandry, 6 Julien Bonnaire, 5 Thibaut Privat, 4 Loic Jacquet, 3 Martin Scelzo, 2 Ti'i Paulo, 1 Thomas Domingo.
Replacements: 16 Mario Ledesma, 17 Lionel Faure, 18 Davit Zirakashvili, 19 Julien Pierre, 20 Elvis Vermeulen, 21 Kevin Senio, 22 Tasesa Lavea, 23 BenoÃ®t Baby.
Leinster: 15 Isa Nacewa, 14 Shane Horgan, 13 Eoin O'Malley, 12 Gordon D'Arcy, 11 Fergus McFadden, 10 Johnny Sexton, 9 Isaac Boss, 8 Jamie Heaslip, 7 Shane Jennings, 6 Sean O'Brien, 5 Nathan Hines, 4 Leo Cullen, 3 Mike Ross, 2 Richardt Strauss, 1 Heinke Van Der Merwe.
Replacements:16 Jason Harris-Wright, 17 Cian Healy, 18 Clint Newland, 19 Devin Toner, 20 Dominic Ryan, 21 Eoin Reddan, 22 Shaun Berne, 23 Dave Kearney,
Referee: Wayne Barnes (RFU)