It was a disappointing end to a day that promised so much as Munster opened brightly and led 7-0 after a well worked Keith Earls try was converted by Ronan O'Gara.

They went in at the break leading 7-3 but re-emerged to produce what was probably their worst 40 minutes at the knock out phase in their long proud history in this competition.

In that second half, their visits to the Biarritz half were rare events while their one opportunity to extend their lead came in the 54th minute when O'Gara's penalty attempt - from inside his own half - fell short.

But for all Biarritz's dominance it wasn't until the 64th minute that they managed to edge ahead, Dimitri Yachvilli landing his third successful penalty after Paul Warwick was badly caught as he attempted to run a ball out of his own 22. Six minutes later, another Yachvilli penalty put five points between the sides and effectively settled this contest.

This was certainly a game Munster looked well capable of winning on the evidence of the opening half when they harried and hassled the home side to good effect. They might have taken the lead in the 19th minute when Jerry Flannery made a great run deep into the Biarritz 22 and had his pass to the supporting O'Gara been a little softer the try was on.

Ten minutes later they got the reward for their adventure when after a storming run from Donncha O'Callaghan, Alan Quinlan carried on and when the ball was moved left James Coughlan delivered the prefect scoring pass to Earls.

O'Gara landed the tap-over conversion and up the end of the field moments later it needed Mick O'Driscoll and Denis Hurley to prevent Benoit August from scoring off a front of line-out move.

Earlier, August's intervention with a blatantly offside big hit on Jean de Villiers seemed certain to offer the opportunity for O'Gara to extend the lead but referee Dave Pearson ignored the plea and incredibly Munster were awarded just one penalty kick at goal in the entire game.

And if the Munster dressing room was a disconsolate place afterwards there was a quiet acceptance that they had been architects of their own downfall.

Besides that hard to fathom second half display, there was the performances by Yachvilli, August and Imanol Harinordoquy that set the tone for this Biarritz victory. If August was menacing all day, Harinordoquy was majestic in everything he did while Yachvilli was the maestro behind a dominant pack who exacted full return when Munster erred.

It was a disappointing end to a day that had started well and now Munster must somehow re-group ahead of the crucial game in Cardiff next Sunday.

Munster: P Warwick, D Hurley, K Earls, J de Villiers, L Mafi; R OGara Capt, T OLeary; M Horan, J Flannery, J Hayes, D OCallaghan, M ODriscoll, A Quinlan, D Wallace, J Coughlan. Replacements: T Buckley for Hayes (57 mins), N Williams for Coughlan (63 mins), N Ronan for Quinlan (71 mins), J Brugnaut for Horan (72 mins), P Stringer for O'Leary (74 mins), S Deasy for D Hurley (75 mins) D Varley for J. Flannery (78 mins), T Gleeson for L Mafi (78mins)

Biarritz Olympique Pays Basque: I Balshaw; T Ngwenya, A Mignardi, A Erinle, J Gobelet; K Hunt, D Yachvili; E Coetzee, B August, C Johnstone, J Thion capt, T Hall, M Lund, W Lauret, I Harinordoquy. Replacements _ M Carizza for Hall (2-5 mins and 67 mins), J Peyrelongue for Erinle (48 mins), F Barcella for Coetzee (60 mins), F Faure for Harinordoquy (66 mins), R Terrain for August (77 mins). Not used: R Hugues, V Courrent, P Bidabe.

Referee: Dave Pearson (England).