The sending off of Scarlets left wing Morgan Stoddart sparked a one-sided second-half in France as Clermont cruised to a 49-16 win on Saturday.
The Scarlets got off to a flying start at the Stade Marcel Michelin as Jonathan Davies scored a try after just three minutes, finishing off a great move that was started by George North and went through the hands of Scott Williams and Rhys Priestland.
Morgan Parra soon got the home side on the scoreboard with two penalties though, the second of which came after Stoddart caught the ball in an offside position and was harshly despatched to the sin bin.
Far from struggling while they were down to 14 men though, the visitors actually extended their lead by six points during that 10 minute period as Priestland kicked a penalty and then took the opportunity to slot over a drop goal from in front of the posts.
It all started to unravel for the Welshmen in the final ten minutes of the first half though. First, Parra broke away after a cleverly worked line-out before finding Sitiveni Sivivatu on his shoulder and the New Zealand international coasted over to score.
And then, with the scores level at 13-13, Stoddart was given a red card after not rolling away from a tackle and lying on the wrong side of the ball to earn his second yellow card of the afternoon.
Clermont were looking like scoring their second try of the game at the time after a great jinking run from Sivivatu but they had to settle for another Parra penalty, which gave them a 16-13 lead at the break.
The prospect of playing an entire half a man short away from home against one of the best sides in Europe is a daunting one and it is no surprise that the Scarlets struggled to live with their opponents in the second half.
The Clermont pack got the ball rolling with a penalty try in the opening couple of minutes and, although Priestland did respond with a penalty, tries from Lee Byrne and Damien Chouly wrapped the bonus point up well before the hour mark.
Byrne had Sivivatu to thank for his try after the big winger provided a deft pass for the Welshman to sprint down the right-hand touchline and Chouly crashed over in the same corner after incessant pressure from the hosts.
Julien Bonnaire took the try count to five in the final 10 minutes, with the French international back row forward finishing off an overlap in the right-hand corner where Stoddart would have been defending. And flying Fijian winger Napolioni Nalaga intercepted a tired pass from Priestland in the last minute to make it six, with Brock James adding the conversion to take the total to one short of 50 and cap a resounding win for the French side.
Tries: Sivivatu, Penalty try, Byrne, Chouly, Bonnaire, Nalaga
Con: Parra 4, James
Pen: Parra 3
Pen: Priestland 2
Sent-off: Morgan Stoddart (two yellow cards)
ASM Clermont Auvergne: 15 Lee Byrne, 14 Sitiveni Sivivatu, 13 Aurelien Rougerie, 12 Wesley Fofana, 11 Naipolioni Nalaga, 10 Brock James, 9 Morgan Parra, 8 Damien Chouly, 7 Gerhard Vosloo, 6 Julien Bonnaire, 5 Nathan Hines, 4 Jamie Cudmore, 3 Davit Zirakashvili, 2 Benjamin Kayser, 1 Thomas Domingo.
Replacements: 16 Ti'i Paulo, 17 Vincent Debaty, 18 Daniel Kotze, 19 Julien Pierre, 20 Elvis Vermeulen, 21 Loic Jacquet, 21 Ludovic Radosavljevic, 22 David Skrela, 23 Benson Stanley.
Scarlets: 15 Liam Williams, 14 George North, 13 Jonathan Davies, 12 Scott Williams, 11 Morgan Stoddart, 10 Rhys Priestland, 9 Tavis Knoyle, 8 Rob McCusker (capt), 7 Josh Turnbull, 6 Aaron Shingler, 5 Johan Snyman, 4 George Earle, 3 Samson Lee, 2 Matthew Rees, 1 Phil John.
Replacements: 16 Ken Owens, 17 Shaun Hopkins, 18 Deacon Manu, 19 Sione Timani, 20 Kieran Murphy, 21 Gareth Davies, 22 Aled Thomas, 23 Gareth Maule.
Referee: Peter Fitzgibbon (Ireland)
Assistant referees: Paul Haycock (Ireland), Simon McDowell (Ireland)
Television match official: Dermot Moloney (Ireland)
Timekeeper: Bruno Bessot (France)
Assessor: Claudio Giacomel (Italy)
Citing commissioner: John Cole (Ireland)