Clermont took a stranglehold on Pool 5 as they defeated Leinster 28-21 at Aviva Stadium in Dublin on Saturday.
It was unpleasant viewing for the home fans, who were hoping for a response from the holders following last week's defeat at Marcel Michelin.
However, a late try from Fergus McFadden did offer some hope of making the knockout stages as they await games against the Scarlets and Exeter knowing that only two victories will do.
Leinster lost hooker Richardt Strauss to a knee injury on eleven minutes which meant Sean Cronin emerged much earlier than home head coach Joe Schmidt would have liked against the physical Clermont pack, a pack he used to lead.
That injury came in between a penalty apiece from Morgan Parra and Jonathan Sexton in a balanced opening seventeen minutes at the Dublin venue.
However, it was to be Parra who would further trouble the scorers before the end of the first quarter as Jamie Heaslip was pinged for entering a ruck from the side. It was a simple three points for Clermont, who knew that an away win would all but seal top spot in Pool 5.
Leinster managed to level matters with fifteen minutes remaining until the half-time break when Clermont were offside after a good bust from Heaslip took the Irish to within five metres. Sexton made no mistake with the ensuing penalty in a nip and tuck opening.
Clermont then turned on the style in the final ten minutes of the half when - after Parra's third penalty - Sitiveni Sivivatu skipped down the left before handing to Lee Byrne who passed to Naipolioni Nalaga. The wing's carry took them to within five metres before recycled ball from Parra saw Wesley Fofana hit the ideal scoring line. Parra's conversion made it 16-6 which was how it stayed until the break as Leinster's Heineken Cup title defence was waning.
Leinster will host the Scarlets before travelling to Exeter in their Pool run-in, but they would not have been looking any further than the here and now and when Parra extended the lead three minutes after the interval, it was becoming worrying as Clermont's class was clear.
Sexton did reduce the deficit back down to ten minutes on 46 minutes although the home cheers were muted when blindside Sean O'Brien was shown yellow for an off-the-ball tackle on Sivivatu. It wasn't quite the final nail in the coffin but it was mighty close to being curtains for the champions, who were being outmuscled in several, if not all, facets of the action.
Parra's resulting three points off the tee from that O'Brien offence made it 22-9 as the match continued to grow into a one-sided affair. The second-choice France scrum-half was at it again ten minutes later as this time Mike Ross was being given a torrid time at the scrum. That was the prop's last act as boss Schmidt knew he could not risk another yellow card.
They did rally when O'Brien returned to the fray and his back-row colleague Shane Jennings gave the home fans hope with a try from a well-worked line-out with quarter of an hour left. Clermont were not to be denied though and another Parra penalty kept the score ticking over as the French never really looked like relinquishing their vice-like grip on the match.
A late yellow card for Julien Bardy gave Leinster a sniff of a losing bonus-point though and that was all the reigning champions needed as they capped a disappointing afternoon with a stunning counter-attack from inside their own half. That passage was finished with Sexton feeding McFadden to score in the corner and the single point could yet prove to be critical.
Tries: Jennings, McFadden
Pen: Sexton 3
Yellow card: Sean O'Brien (50 mins)
Pen: Parra 7
Yellow card: Julien Bardy (74 mins)
Leinster: 15 Ian Madigan, 14 Fergus McFadden, 13 Gordon D'Arcy, 12 Andrew Goodman, 11 Isa Nacewa, 10 Jonathan Sexton, 9 Eoin Reddan, 8 Jamie Heaslip, 7 Shane Jennings, 6 Sean O'Brien, 5 Damien Browne, 4 Leo Cullen (capt), 3 Mike Ross, 2 Richardt Strauss, 1 Heinke Van Der Merwe.
Replacements: 16 Sean Cronin, 17 Cian Healy, 18 Michael Bent, 19 Devin Toner, 20 Kevin McLaughlin, 21 Issac Boss, 22 Andrew Conway, 23 David Kearney.
Clermont: 15 Lee Byrne, 14 Sitiveni Sivivatu, 13 Aurélien Rougerie (c), 12 Wesley Fofana, 11 Naipolioni Nalaga, 10 Brock James, 9 Morgan Parra, 8 Damien Chouly, 7 Julien Bardy, 6 Julien Bonnaire, 5 Nathan Hines, 4 Jamie Cudmore, 3 Davit Zirakashvili, 2 Benjamin Kayser, 1 Raphael Chaume.
Replacements: 16 Ti'i Paulo, 17 Vincent Debaty, 18 Daniel Kotze, 19 Loïc Jacquet, 20 Alexandre Lapandry, 21 Ludo Radosavljevic, 22 David Skrela, 23 Regan King.
Referee: Wayne Barnes (England)
Assistant referees: Martin Fox (England), Paul Dix (England)
Television match official: Geoff Warren (England)