Biarritz were chasing tries from the start - and amassed thirteen in a hugely impressive performance, albeit against one of the weakest sides in the competition.
But it was ignominy for Cardiff as they join Italian club Viadana as the only teams to record defeats in all their Heineken Cup matches this season.
Cardiff took an early lead with a try when Wales international wing Craig Morgan crossed after only two minutes. The flyer took advantage of a ricochet off a French shoulder from a Nicky Robinson kick and he ran 40 metres to the posts for Robinson to convert.
But the lead lasted just three minutes as Biarritz took a penalty to touch, won the linout and drove skipper Thomas Lievremont over which scrum half Dimitri Yachvili converted to level the scores at seven apiece.
In the 10th minute Biarritz scored their second through Marc Stcherbina and again Yachvili added the extra points.
But it seemed as this may be the day that Cardiff broke their Hieneken duck as they put together some determined rugby that resulted in Robinson notching a 40-metre penalty draw closer at 14-10.
But that was to be the end of Cardiff's resistance. Constant Biarritz pressure on the away line saw Cardiff take the maul down and a penalty try awarded. Yachvili goaled that and again on the half-hour as Bernat-Salles opened out from a lineout on his own line and eight pairs of hands were involved before the former French skipper, lock Olivier Roumat, crossed.
Then, after Morgan was yellow-carded for preventing a Bernat-Salles try, 17-stones prop Damian Minassian ran 40 metres past four 'tacklers' to score under the posts and Yachvili again converted.
A Robinson penalty from 30 metres was replied by a sixth try just on the interval as classy Nicolas Brusque scored in the corner but took a knee as he did and fists flew with Brusque being taken off.
When Cardiff's start to the second half missed touch, Bernat-Salles ran it out, caught his own kick and sent replacement Michael Etcheverria over on his first touch. Biarritz declined the conversion.
With de Santis letting Biarritz run, lock Ovidiu Tonta was over, but scrum half Ryan Powell nicked one for Cardiff that Robinson converted.
Back came Biarritz with hooker Julien Campo making the corner and replacement Sylvain Betsen getting the tenth try, just as Peter Rogers was given the Cardiff hooking role, something he had not done for ten years.
Messages came that 13 tries were needed and though David Dewdney scored a third try for Cardiff, Bernat-Salles, Giullaume Bousses and Bernat-Salles again in injury time gave Biarritz their chance to go through.
Biarritz Olympique 75 Cardiff 25
HT: 40-13 Attendance: 4,000
Biarritz Olympique: Tries - P Bernat-Salles 2, T Lievremont; M Stcherbina, O Roumat, D Minassian, N Brusque. O Tonita, J Campo, S Betsen, G Bousses, M Etcheverria, Penalty try; Cons - D Yachvili 5
Cardiff: Tries - C Morgan, R Powell, D Dewdney; Cons - N Robinson 2; Pens - N Robinson 2