Bordeaux-Begles' thumping 34-7 victory over Brive was enough to secure seventh position and a place in next season's Champions Cup for Raphael Ibanez's men.
Montpellier's triumph in the Challenge Cup opened up an extra berth for the Top 14 and tries from Matthew Clarkin, Metuisela Talebula, Louis-Benoit Madaule and Nans Ducuing steered Bordeaux to the win they needed to snare it.
Castres, meanwhile, remain one place above Bordeaux in sixth following their hard-fought 25-20 victory at relegated Oyonnax.
The visitors were trailing 17-9 at the break, but fought their way back in the second half via three further penalties from Rory Kockott who also converted David Smith's vital late try.
Stade Francais' disappointing season continued as they laboured to an unconvincing 28-26 win over relegated Agen.
Jules Plisson's late penalty saved the home side's blushes at the MM Arena after Marc Baget-Rabarou, Tamaz Mchedlidze, Antoine Miquel and Marco Kotze had all crossed for the visitors.
France wing Djibril Camara scored two of Stade's three tries, with Jeremy Sinzelle claiming the other.
Elsewhere, New Zealand fly-half Colin Slade bagged two tries as 11th-placed Pau downed 10th-placed Grenoble 29-12.
Charly Malie also found the line for the home side, while the visitors were kept try-less.
Sunday's two games see leaders Clermont-Auvergne visit Toulouse and Montpellier host Toulon.