Their lead at the head of the standings has been cut to just one point at the halfway mark, though, and another defeat this week would leave Biarritz as favourites to reach the quarter-finals given that Sale still have to travel to the Parc des Sports Aguiléra in Round 6.
Steve Diamond's men did pick up what could be a crucial losing bonus point last time out, however, as a last-gasp drop goal from Joe Ford saw them get back within seven points of the tournament newcomers.
Friday's fixture was Oyonnax' first victory in Europe following a home draw with Worcester and a convincing defeat at Biarritz and it re-ignited their slim hopes of making the knockout stages in their maiden campaign.
But, while an Oyonnax win was far from surprising given that they have a formidable record on home soil having toppled Heineken Cup holders RC Toulon, runners up ASM Clermont Auvergne, French Champions Castres Olympique, Perpignan and Biarritz in front of their own fans in the Top 14 this term, a repeat in Round 4 would be a major surprise when you look at their form on the road.
Oyonnax haven't avoided defeat away from home all season, with Bayonne, Racing Metro, Bordeaux-Begles, Montpellier, Grenoble and Toulouse all beating them in the league in the past three months and Biarritz doing likewise in Europe.