The Scarlets put poor Celtic League form behind them as they turned on their European style at Stradey to beat Glasgow by thirty points.
Wales scrum half Dwayne Peel scored two tries, with winger Garan Evans, flanker Ian Boobyer and prop Martyn Madden the other Llanelli try scorers in a second half romp.
Playing into the stiff breeze in the first half, the Scarlets were happy to go into the break a point ahead (11-10) after withstanding some heavy Glasgow pressure.
Wales outside half Stepehn Jones kicked 17 points and his replacement Gareth Bowen chipped in with a penalty to complete the scoring.
Lock Jason White and flanker Donnie Macfadyen went over for tries for Glasgow, with Tommy Hayes adding a conversion and a penalty.
CARDIFF 15 BIARITTZ 26
Ill-discipline and a powerful Biarritz pack cost Cardiff a winning start to the Heineken Cup at the Arms Park tonight.
Consistent penalties, particularly by the front row, resulted in Cardiff prop Peter Rogers being yellow-carded early in the second half.
His absence proved costly, with visiting flanker Christophe Milheres powering over for a try in the corner, and scrum-half Dimitri Yachvili's superb sideline conversion gave Biarritz a valuable seven-point lead.
Home fly-half Iestyn Harris slotted his fifth penalty goal of the night to narrow the gap to four, but didn't have the penetration to score the all-important try.
Biarritz did, and veteran winger Philippe Bernat-Salles put the match beyond doubt with a last-minute try.
Cardiff opened the scoring with a third-minute Iestyn Harris penalty goal, but were forced to soak up intense pressure from the Frenchmen in the tryless opening half, with Bernat-Salles proving particularly dangerous.
Fullback Rhys Williams snuffed out one attack with a fine tackle before relieving the tension with a massive 55-metre clearing kick, but not many of his team-mates walked off at halftime proud of their defence.
Harris and Yachvili (2) traded penalty goals as English referee Chris White stamped his mark on the game, and despite having little ball or territory, a monster 52-metre penalty goal from Harris in the 34th minute gave the home side a three-point lead at the break.
Cardiff centre Matt Allen was stretchered off late in the match after being knocked out in a tackle.
MONTFERRAND 47 SWANSEA 12
Swansea went the same way as every other team that has visited Montferrand in European competitions as they became the home side's 20th victim at Parc des Sports Marcel-Michelin.
For the second weekend in a row, the Whites were reduced to 13 men when replacement flanker Dean Thomas and American prop Dan Dorsey were yellow-carded in the second half.
Home captain Olivier Magne was in dominant form, scoring two of his sides six tries, and Sebastian Viars' 17 points with the boot was enough to earn him the Heineken Man-of-the-Match award.
Swansea went into the match knowing Montferrand were unbeaten in 19 matches against in both the Heineken Cup and European Shield at home, and knew they averaged 47 points in the process. Both records remained intact.
Heineken Cup scoring details
Scorers: Montferrand: Tries: O Magne 2, S Bozzi, R Cockerill, E Vermeulen, J Marlu; Pens: S Viars 2; Cons: S Viars 4; DG - S Viars. Swansea: Pens: G Henson 4.
Scorers: Llanelli: Tries: D Peel 2, G Evans, I Boobyer, M Madden; Cons: S Jones 4; Pens: S Jones 3, G Bowen. Glasgow: Tries: J White, D Macfadyen.
Cardiff: Pens - I Harris 5.
Biarritz: Tries - C Milheres, P Bernat-Salles; Pens - D Yachvili 4; Cons - D Yachvili 2. Halftime: Cardiff 9-6.