Racing 92 crushed Agen 42-13, while there were also Top 14 wins for Lyon, Castres, La Rochelle, Pau, Clermont and Brive.
Log leaders Montpellier and Racing have now been confirmed as hosts of the two semi-finals.
Racing led 28-13 at half-time and kept Agen scoreless in the second half. Wing Juan Imhoff scored a brace for the winners.
Elsewhere, Lyon claimed a 32-24 triumph over Montpellier, who fielded a second-string lineup because they had already secured top spot.
More importantly, from a South African point of view, centre Jan Serfontein was back and playing well for Montpellier after a mysterious injury scare kept him sidelined last week.
In other notable results, Castres lashed Oyonnax 54-3 to clinch the last available spot in the playoffs at the expense of La Rochelle, who humbled Stade Français 31-7. Despite the defeat, Stade still managed to finish 12th, three points clear of Oyonnax, who will now have to compete in a relegation playoff match. Stade are safe from a potential drop to the Pro D2.
Already sure of a place in the semi-finals, Toulon sent out a weakened side and lost 38-26 against Pau, while Clermont shocked Toulouse 36-26, with Flip van der Merwe opening scoring for the winners.
Pro D2-bound Brive beat Bordeaux 22-20 in their last match in top-flight rugby for at least another season.
Round 26 results:
Racing 42 Agen 13
Lyon 32 Montpellier 24
Castres 54 Oyonnax 3
La Rochelle 31 Stade Français 7
Pau 38 Toulon 26
Clermont 36 Toulouse 26
Brive 22 Bordeaux 20
Toulouse vs Castres
Toulon vs Lyon
Montpellier vs TBC
Racing 92 vs TBC