Another epic to add to the list between these heavyweight contenders.
Unlike last May's classic semi-final in Bordeaux, there was no knockout blow but back-to-back champions Leinster, are undoubtedly feeling a little punch-drunk after a wonderfully defiant effort – Fergus McFadden was particularly outstanding – which saw them concede their proud 17-match unbeaten European record.
These two will joust once more in just five days' time at Lansdowne Road but the French giants clearly hold the upper hand ahead of that latest renewal, with this narrow victory stretching their lead in Pool 5 to a formidable five points.
With the Scarlets seemingly folding their tents at the halfway stage, Leinster's trip to Exeter's Sandy Park after Christmas now seems decisive and will surely indicate whether Joe Schmidt's side can emerge from this pool.
Leinster know that victory next weekend is well within their compass, hardening the sense of frustration at the manner of yesterday's defeat which, although tryless, certainly offered up enough chances for them to puncture Clermont's renowned fortress.
That said, Clermont sniffed blood themselves too on a few occasions, and their route to the whitewash was more often brimful of deadlier intent, only floundering in the face of some formidable defensive efforts from the blue wall.
Leinster brought a few new tricks to the party, with some lovely switch moves featuring heavily, but often they were undone by silly errors and, after Sean Cronin's departure, they will rue an appalling hat-trick of errant line-outs from new Irish international Richardt Strauss.
Aside from Shane Jennings and Eoin Reddan, a weakened, injury-enforced bench held little impact and Schmidt was clearly reluctant to delve deeper than he did, but those he did rely on as starters – particularly Ian Madigan and Andrew Goodman – filled the breach with reasonable effectiveness despite some defensive lapses.
While Clermont will probably still bemoan the line-out that never was at the death – Morgan Parra once more assuming that he, and not Nigel Owens, was, in fact, refereeing – they were still chuffed at a potentially decisive win against their now almost perennial nemesis.
Still, the manner in which Clermont visibly tightened up in the last quarter on attack, conscious that the narrow margin of three points afforded them little margin for error, will offer some succour to Leinster.
The Blues surely cannot compile such a lengthy list of indiscretions in possession in the return leg, and their line-out cannot implode once more; Goodman's understanding in defence is bound to improve and Sean O'Brien, understandably underpowered as he continues his comeback, will have benefited from a nuggety 80 minutes of work.
The first-half narrative followed a statistically quirky theme, with all eight penalties conceded – four from each side – being within kickable range, with Sexton missing the only kick of the half before Clermont, with a penalty advantage, secured the significant half-time breathing space thanks to Brock James' drop goal.
Behind the numbers, the rugby was never less than compelling, as each side danced around the pitch, resembling the heavyweight contenders for this European crown that they undoubtedly are, each seeking to land the forceful blow that might explode the contest into life.
Leinster's rugby was easier on the eye, whereas the home side were more brutish upon impact and they easily made more line-breaks and offloads than the visitors.
However, Leinster seemed to dominate both territory and possession, further backboning the contention that this may have been an opportunity for them to decisively alter the momentum of this pool.
Worryingly, Clermont's opening blow came via a penalty conceded by Mike Ross at scrum time but it seemed that the damage there would not be enduring as the eight settled into a much better rhythm thereafter.
The only penalty miss of the half from Sexton worried the 800 or so Leinster fans amid the cauldron containing 17,760 captivated supporters, as a further brace from Parra eased his side into a 9-3 lead by the 34th minute.
McFadden saved Goodman's blushes – after his missed tackle on Napolioni Nalaga – in the lead-up to the first, while Isaac Boss was particularly scathing of his colleagues for not chasing his box-kick for the second.
Leinster's response was impressive however, as they eked out some vital inches in some intensive trench warfare before Davit Zirakashvili was penalised for a flailing leg in a ruck, allowing Sexton to halve the deficit.
But the home side finished much the stronger before tea-time, with Parra's fourth penalty and James' drop goal – while playing an advantage after a Leinster infringement – sealing a formidable-looking half-time lead.
Leinster visibly upped the physical stakes in the third quarter though, particularly at scrum time, winning two penalties, from the first of which Sexton gambled on an audacious cross-kick to a well-marked McFadden.
McFadden did reach the ball first but he knocked on; Leinster may yet rue what effectively turned out to be the concession of two points, albeit Schmidt conceded that a penalty was no gimme given the condition of the pitch.
It indicated that Leinster were sensing a weakness in Clermont and that they fancied their chances of an upset.
The scrum set the tone and, after Sexton's (pictured left) ambition had been rebuffed by the first penalty win, he dutifully accepted the opportunity to punish Clermont with the three points in the 54th minute when Clermont's eight concertinaed.
There was no scoring thereafter but that was not without the expending of magnificent effort on both sides.
The champions are not on their knees. But they are on the ropes. Now they must come out fighting next week to keep alive their dreams of an unprecedented hat-trick of titles.
ASM Clermont Auvergne – L Byrne; S Sivivatu, A Rougerie (capt), W Fofana, N Nalaga; B James, M Parra; V Debaty (R Chaume 54), B Kayser (T Paulo 60), D Zirakashvili (D Kotze 61); J Cudmore (J Pierre 67), N Hines; J Bonnaire (J Bardy 79), A Lapandry, D Chouly.
Leinster – I Madigan; F McFadden, G D'Arcy, A Goodman, I Nacewa; J Sexton, I Boss (E Reddan 66); C Healy, S Cronin (R Strauss 49), M Ross; L Cullen (capt), D Browne (D Toner 57); K McLaughlin, S O'Brien (S Jennings 66), J Heaslip.
Ref – N Owens (Wales).