Blues (9) 21
Pens: Blair 5. DGs: N Robinson 2.
Biarritz (10) 17
Tries: Traille, Peyrelongue. Cons: Peyrelongue 2. Pen: Peyrelongue.
Full-back Ben Blair kicked five out of six of his penalties for the Blues
Ben Blair struck 15 points as Cardiff Blues held off a misfiring Biarritz in a scrappy Heineken Cup encounter.
The French visitors scored both the game's tries, Damien Traille and Julien Peyrelongue crossing in each half as the lead changed hands several times.
Peyrelongue converted both and added a penalty, but the Blues were indebted to Blair as the full-back kicked five out of six of his attempts at goal.
Fly-half Nick Robinson also added two crucial drop-goals for the Blues.
Blues entered this third round of matches sitting pretty at the top of Pool 6 with a maximum 10 points, having gained bonus-point wins over Calvisano and then Gloucester.
Biarritz had lost at Gloucester then won handsomely at home to Italian side Calvisano, but have been struggling domestically in the French Top 14.
A decent start by the Blues would have asked some hard questions of Biarritz's fragile confidence, but instead it was the French visitors who bossed the opening exchanges.
Some forthright defence strangled any Welsh attempts to move the ball and after 19 minutes earned the first score.
Blues fly-half Robinson tried to force an off-load and gifted possession to Biarritz deep in his own half.
We'd certainly have settled for 14 points out of 15 at this stage
Blues director of rugby Dai Young
A swift transfer to the wing saw Takudzwa Ngwenya make ground before play was switched inside and Traille arced back to go over near the left corner.
The France centre pretended to ground the ball before getting to his feet and heading nearer the posts, getting a clip from Gareth Williams for his cheek as he finally touched the ball to grass.
Peyrelongue accepted the easier conversion, but Blair got things moving for the Blues when he replied with a penalty soon after.
Biarritz were unfortunate not to score a second try when Ngwenya just knocked on as he dived for a chip through, but Peyrelongue stretched their lead with a penalty.
The Blues had been thoroughly stifled but with the first half running out pulled themselves back to within a point.
First Blair calmly stroked over his second penalty, before Robinson clipped over a snap drop-goal to reduce the deficit to 9-10.
If the home side had scarcely deserved their near-parity at the break, the Blues started the second half far brighter.
A third Blair penalty rewarded some early dominance and drive, before Jason Spice scythed through a gap before bearing down on Biarritz full-back Benjamin Thiery.
Andy Powell, fresh from some barn-storming displays for Wales, was on hand to take the scoring pass, only for his scrum-half to spin the ball behind his supporting number eight.
Robinson again struck with a drop-goal, determined to turn any territorial gain into points, to give the Blues a 15-10 lead.
Peyrelongue attempted to reply in kind with an untidy effort that at first sight seemed to have dipped just under the crossbar.
Referee George Clancy sensibly went to the video replay, which seemed to suggest the ball had instead gone over, only for the final decision to controversially go against the French fly-half.
But Peyrelongue made instant amends as Biarritz ran back a poor Blues 22 drop-out, darting through a huge hole - as Robinson and Tom Shanklin got their drift defence all wrong - to score a try he converted himself.
Trailing 17-15 the Blues again edged themselves back in front through the boot of Blair, the New Zealander full-back kicking six more points and being just short with a third long-range effort.
Biarritz threatened sporadically to retake the lead but each time poor handling or poor decisions held them back.
A late scuffle between Biarritz captain Jerome Thion and Maama Molitika saw the Blues back-row - despite blood streaming from his nose - sin-binned to leave the Welsh a man short for the last five minutes.
But the Blues held on for a scrappy win, although Biarritz have a precious losing bonus point to take back to France for next weekend's return fixture.
Cardiff Blues director of rugby Dai Young:
"We'd certainly have settled for 14 points out of 15 at this stage in the group, we certainly didn't play well but a win's a win.
"We struggled to get penetration, struggled to get behind them - all credit to the Biarritz defence, but at the end of the day you've just got to win.
"We showed a lot of character. We knew we weren't playing well, but we hung in there. Maybe two or three years ago we might not have won that."
Biarritz coach John Isaac:
"We're disappointed not to have won the match, but we're glad to go home with a losing bonus point.
"We were expecting a bit more from the Blues, to be honest, but our defence was very good and very aggressive and probably forced them to play a tighter game."
Cardiff Blues: Blair; Halfpenny, Robinson, Shanklin, G Thomas; Robinson, Spice; G Jenkins, G Williams, G Powell, D Jones, Tito (capt), Molitika, M Williams, A Powell.
Replacements: Filise for G Powell (70), T Thomas for G Williams (70), S Morgan, R Sowden-Taylor, Allinson, Sweeney, James for Halfpenny (75).
Sin Bin: Molitika (75).
Biarritz Olympique: Thiery; Ngwenya, Bidabe, Traille, Bolakoro; Peyrelongue, Cibray; Barcella, Noirot, Moala, Thion (capt), Hall, Som, Dridi, Harinordoquy.
Replacements: August for Noirot (53), Coetzee for Barcella (16), Damiani, Lauret for Hall (50), Cabannes for Peyrelongue (79).
Not used: Roidot, Tranier.
Referee: George Clancy (Ireland).