Connacht's quarter-final hopes sank in the French mud as Biarritz battled to an ugly win in atrocious conditions.
There had been doubts whether the game would go ahead following hours of torrential rain in Basque country and the weather ended any prospect of an open encounter.
But Biarritz and their powerful pack were superior in their handling of the elements and they ground out a much-needed victory thanks to Iain Balshaw's try and the boot of Dimitri Yachvili, before Seremaia Burotu rubbed salt into Connacht's wounds with a late try.
Connacht had won 22-14 a week earlier, and while the victory was celebrated with beers and cheers in Galway, it signalled the end of the road for Biarritz's coaches.
Eric Elwood made just one change, with flanker Jonny O'Connor replacing the injured Willie Faloon.
Connacht did not escape their own controversy this week and they have become embroiled in a war of words with Leinster following the news that Mike McCarthy will join the Heineken Cup champions in the summer.
The Ireland second- row's departure will be a major loss for the Galway outfit. He demonstrated his commitment to Connacht with a colossal work-rate but it was not enough to inspire Elwood's men to a first away victory in the Heineken Cup – although they still have a tiny chance of progress, and the Amlin Challenge Cup remains a very real possibility.
It took Biarritz just two minutes to open the scoring after O'Connor was penalised at the breakdown and Yachvili slotted the simple penalty.
The fired-up Basques continued to dominate the opening exchanges as Connacht battled to hang on.
Biarritz kicked to the corner as they looked to land a killer blow. They releasing Taku Ngwenya on the right, but the American flyer failed to ground the ball.
Connacht constantly thwarted Biarritz and they weathered the storm, with the French club unable to stretch their lead.
Both sides struggled to cope with the wet ball and were undone by unforced errors, but Biarritz eventually defied the elements.
They launched a sweeping backs move from the back of a dominant scrum with Traille creating the opening after Dan Parks came flying out of the defensive line. The France centre fed Jean-Pascal Barraque, who drew Robbie Henshaw to release Balshaw for an aquatic dive.
Connacht almost conceded a quick-fire second as scrum-half Kieran Marmon lost the ball in his own '22'. Traille attempted to hack through but was unable to kick the ball out of the standing water on the pitch.
Yachvili was off target minutes before the break and Connacht were fortunate to go into the changing rooms trailing by just 10 points.
Biarritz again came out firing from the restart and they launched a succession of powerful attacks. But once more they were unable to capitalise on all their territory and possession.
They were dealt a blow on 47 minutes as hooker Benoit August was sent to the sin-bin for persistent infringements, but Connacht failed to punish the hosts for their indiscretion as Parks sliced his kick at goal.
Yachvili continued to pull the strings, but the encounter was brought to a halt after Connacht centre Danie Poolman suffered a serious injury.
The South African centre caught a knee to the head after taking the ball into contact and received prolonged treatment on the pitch before being stretchered off in a neck brace.
Biarritz turned the screw on the hour mark and threatened to grab a second try after their giant ball-carriers put Connacht on the back foot.
Biarritz survived their period down to 14 men without conceding a point but within minutes of returning to full complement they shot themselves in the foot.
Sub Thibault Dubarry had been on the pitch for less than 10 minutes when he was shown yellow for being over zealous at the breakdown.
But Connacht remained camped in their own half and the two-time Heineken Cup finalists were rewarded for their dominant performance as Burotu scored at the death.
Biarritz – I Balshaw; T Ngwenya, J Barraque(S Burotu 76), D Traille, A Brew; J Peyrelongue, D Yachvili; F Barcella (L Blaauw 72), B August (J Genevois 66), F Kodela (T Synaeghel 60), E Lund, P Taele, W Lauret( M Lund 72), R Lakafia (J Genevois 49-59), I Harinordoquy (capt, T Dubarry 56).
Connacht – R Henshaw, T O'Halloran, D Poolman (M Jarvis 56), D McSharry, F Vainikolo; D Parks (capt) (M Nikora 68), K Marmion (P O'Donohoe 56), B Wilkinson (D Buckley 57), J Harris Wright (E Reynecke 66), R Loughney (N White 48), M Kearney (G Naoupu 48), M McCarthy, A Browne (D Qualter 76), J O'Connor, E McKeon.
Ref – L Hodges (WRU)