Genuine chances were hard to come by at the Stade Chaban-Delmas, and the Spaniards will be regarded as favourites going into next week’s second leg after containing the hosts with some ease.
Neither goalkeeper was seriously troubled in a match that saw Les Girondins dominate possession but struggle to find an end product.
What little football there was in a forgettable first half came from Bordeaux, although clear-cut chances were few and far between.
A bobbly, uneven surface did not help matters, but Osasuna striker Pierre Webo was able to rise in the ninth minute to glance a header straight at home goalkeeper Ulrich Rame.
The hosts probed away, but aside from a low, 12-yard Pablo Francia shot in the 19th minute that was easy for Osasuna goalkeeper Ricardo Lopez, they offered precious little in the final third.
In the 44th minute, Marouane Chamakh, arguably the liveliest player on the pitch, almost got on the end of a whipped David Jemmali cross from the right, but the Bordeaux striker was just inches away from applying a final touch from close range.
The second half followed in much the same vein, with Osasuna happy to sit back and soak up the pressure.
Bordeaux coach Ricardo tried to liven things up by introducing striker Edixon Perea from the bench, at the expense of the ineffective Vladimir Smicer, but the Spaniards remained solid at the back.
Javier Flano almost ruined that when his heavy back-pass came at Ricardo at chest height, but the goalkeeper was just about able to clear his lines as Bordeaux’s forwards closed in.
Julien Faubert then found some rare space on the edge of the Osasuna area in the 74th minute, but his left-foot shot was gobbled up by Ricardo.
And in the 80th minute, Bordeaux replacement Florian Marange attempted a long-range effort, but it flew wide of the target as the visitors held out.