Cardiff remain top of Pool Six after a workmanlike 10-6 victory over Biarritz at Parc des Sports Aguilera.
Jamie Robinson scored the game's only try after 13 minutes as Cardiff produced a stern defensive display to clinch just their second win in France.
Biarritz hit back through penalties from Damien Traille and Julien Peyrelongue but the result stretched Cardiff's unbeaten run in the pool to four games and left them on the verge of qualification for the quarter-finals.
In Group Six's other game Gloucester recorded the biggest winning margin of the day when they defeated Calvisano 48-5 at Kingsholm. First-half tries from Mark Foster and Luke Narraway put the home side on the way before a brace of tries from Lesley Vainikolo and Matthew Watkins ensured an emphatic victory.
In Pool Three Ospreys had a comfortable 36-16 win over Italian side Treviso at the Stadio Comunale di Monigo to continue their quest for a quarter-final place.
Tries from Sonny Parker (two), Alun Wyn Jones, Jonathan Thomas and Filo Tiatia ensured the Welsh side came away with a predictable bonus-point win against a limited Treviso side.
Elsewhere Toulouse piled the pressure on Heineken Cup rivals Bath as they moved closer to a place in this season's quarter-finals.
The three-time European champions eased seven points clear in Pool Five – closest challengers Bath visit Glasgow today – after subduing a spirited Dragons effort at Rodney Parade 26-13.
Tries during the opening flurries of each half by wings Maxime Medard and Cedric Heymans emphasised a gulf in class, although Toulouse still had to dig deep.
Frederic Michalak kicked a drop-goal and two penalties that underlined early Toulouse dominance, while David Skrela converted Medard's fourth-minute touchdown, yet the Dragons gave it their best shot.