Munster were dumped out of the Heineken Cup at Stade Anoeta as Dimitri Yachvili booted Biarritz to an 18-7 win and into an all-French final in Paris.
Two-time champions Munster were firmly in control after a slick try from Keith Earls, converted by Ronan O'Gara, helped them establish a 7-3 interval lead.
But Biarritz, who included English trio Iain Balshaw, Magnus Lund and Ayoola Erinle in their starting line-up, ground them into submission in the second half. They never seriously threatened the whitewash but with Munster falling foul of referee David Pearson's whistle and Yachvili kicking the penalties - six from six attempts - they crept in front.
Starved of possession and struggling to escape their own half, the Irish province faded from contention to ensure their search for a first win in San Sebastian continues.
Biarritz have endured a poor season in the French Top 14 with their seventh-place finish not enough to qualify for next season's Heineken Cup, making victory all the more crucial.
It was a scrappy match, marred by a succession of handling errors that were not entirely explained by the heavy rain that preceded the match.
The repeat of the 2006 final, which Munster edged 23-19 to win their first Heineken Cup title, failed to live up to expectation but remained tense until Biarritz pulled clear late on.
Munster scored the only try of the game when Donnacha O'Callaghan marauded into space, the superb Alan Quinlan kept the move going before Jerry Flannery distributed wide where David Wallace supplied the scoring pass to Earls.