Ronan O'Gara's La Rochelle prevailed 31-13 at Bordeaux in an all-Top 14 clash in the Heineken Champions Cup which defied domestic form.
Five tries lit up a lively last-16 first leg at Stade Chaban-Delmas that saw La Rochelle pull away in the third quarter.
Raymond Rhule and Jonathan Danty touched down for the visitors, who were also awarded a penalty try, while Ihaia West slotted four penalties.
Cameron Woki and Federico Mori crossed for Bordeaux, who sit a place higher than their opponents in the French league.
Former Munster and Ireland out-half O'Gara was not present on the sidelines for the victory as the La Rochelle head coach serves a two-week suspension for "indiscipline, in particular for challenging the decisions of match officials", incurred against Racing 92.
The result puts La Rochelle in a strong position to qualify for the quarter-finals, with the second leg to be played at the Stade Marcel Deflandre next Saturday.
