Pau closed the gap on Pool Two leaders Worcester Warriors to one point with a 21-6 European Challenge Cup victory over the Premiership club at Stade du Hameau on Friday.
The Top 14 outfit entered matchday three sitting third in the group but climbed above the Ospreys ahead of the Welsh region's clash with Stade Francais at the Liberty Stadium on Saturday.
Colin Slade scored two of Pau's three tries, including one touchdown in the first minute, with Julien Blanc adding the third in the closing stages.
Two first-half penalties from the boot of Jamie Shillcock to make it 7-6 at half-time was all the visitors could muster, before the home side built a cushion.
In the day's other fixture between the bottom two sides in Pool Three, Grenoble got the better of Agen 22-15 to temporarily go top.
Benetton and Harlequins meet in Treviso on Saturday to determine who will sit at the summit by the end of the weekend.