Clermont 48 (20)
Dwayne Peel is tackled by Clermont's Laurent Emmanuelli
Tries: Rougerie 3, Malzieu, Bonnaire, B James, Domingo.
Cons: James 4, A King.
Scarlets 21 (7)
Tries: D James, Peel, R King.
Cons: S Jones 2.
Llanelli Scarlets came up short in France against a Clermont Auvergne side that outpaced and outmuscled their Heineken Cup visitors from Wales.
Clermont captain Aurelien Rougerie got two tries before the break, with fellow wing Julien Malzieu also crossing.
Dafydd James scored for the Scarlets but they trailed 20-7 at half-time.
Julien Bonnaire got a fourth for the French, Scarlets replied through Dwayne Peel and Regan King, but three more Clermont tries sealed a French win.
Rougerie claimed his hat-trick, before fly-half Brock James and replacement prop Thomas Domingo also crossed for tries.
After an early penalty from James, Clermont captain Rougerie extended their lead with a cheeky interception try.
The wing read a long pass from Scarlets fly-half Stephen Jones - hardly surprising as the two were team-mates at the Parc des Sports Marcel-Michelin for two seasons - and romped away under the posts.
We had a great time out there and it's a fantastic start to our European campaign
Clermont captain Aurelien Rougerie
But Scarlets hit back immediately thanks to a sublime break from King, the centre handing off Alexandre Audebert to send Dafydd James over in the right corner.
After a nervous wait for the TMO to confirm the grounding of the ball, Jones kicked a fine conversion to leave the Welsh trailing 10-7 after 20 minutes.
Both sides were committed to trying to play with flair and it made for an exciting encounter.
Clermont fly-half James nearly fashioned a score with a clever chip-and-chase down the left, but Morgan Stoddart was alert to the danger.
Yet the Scarlets failed to learn that lesson and James chipped through again, although this time for Malzieu who raced past a labouring Dafydd James to touch down.
Before the half-hour mark Clermont had their third try, open-side flanker Audebert providing the link to allow Rougerie to force his way over for his second try.
Thankfully for the visitors Brock James missed both conversions, but a 20-7 gap at half-time still looked ominous for the Scarlets.
It took less than five minutes after the restart for Clermont to seal a bonus point, as blind-side flanker Bonnaire went over from close range.
A brilliant solo effort from Peel, the scrum-half scorching under the posts after taking a line-out tap down, suggested the Scarlets were not yet out of it.
And that was confirmed as a flowing move from right to left sucked in the French cover, allowing King to gather and run in another seven-pointer.
But back came Clermont again, Gonzalo Canale chasing through Brock James' kick to gather - with a suspicion of a knock-on - before the ball went out to the right for Rougerie to claim his hat-trick.
James' conversion made it 34-21 to Clermont, before the fly-half raced through for a try of his own that stretched the home side's lead to 20 points.
Scarlets' best chance of taking something out of the match now realistically rested with a fourth try for a bonus point.
But the French powered their way to the end of the match, the strength of their squad such that they were able to bring on South Africa's World Cup-winning captain John Smit at hooker.
Replacement prop Domingo claimed a seventh Clermont try - former Wasps man Alex King converting - to cap a fine performance and leave them top of Pool Five.
Clermont captain Aurelien Rougerie:
"We had a great time out there and it's a fantastic start to our European campaign.
"We definitely weren't perfect, and we've got lots to look at and work on for next week. It certainly wasn't an easy game.
"But I think we've come out tonight and we've said: 'We're here and we're right in this pool'."
Scarlets director of rugby Phil Davies:
"We let them get away in the beginning of the second half. We gave ourselves some real momentum towards the end, but it was too late to change the result.
"We're obviously disappointed not to have a bonus point, particularly in a pool this tough.
"We always feel we can win a game, but we made a lot of mistakes that we don't usually make."
Clermont Auvergne: Anthony Floch; Aurelien Rougerie (capt), Gonzalo Canale, Pierre-Manuel Garcia, Julien Malzieu; Brock James, Pierre Mignoni; Laurent Emmanuelli, Mario Ledesma, Martin Scelzo, Loic Jacquet, Thibaut Privat, Julien Bonnaire, Alexandre Audebert, Elvis Vermeulen.
Replacements: John Smit for Ledesma (59), Thomas Domingo for Emmanuelli (22), Christophe Samson for Privat (75), Emmanuel Etien, Arnaud Pic, Alex King for James (67), Grant Esterhuizen for Canale (70).
Scarlets: Morgan Stoddart; Dafydd James, Regan King, Gavin Evans, Matthew Watkins; Stephen Jones, Dwayne Peel (capt); Iestyn Thomas, Matthew Rees, Deacon Manu, Vernon Cooper, Scott MacLeod, James Bater, Gavin Thomas, Alix Popham.
Replacements: James Hayter for Rees (64), Bruce Douglas, Adam Eustace for Cooper (64), Dafydd Jones, Gavin Cattle, Rhys Priestland, Garan Evans for James (51).
Referee: Chris White (England).