Racing seals Top 14 semi-final spot
Racing 92 thrashed Agen 42-13 to ensure it claimed second place in Top 14 and an automatic place in the semi-finals, while Castres thrashed Oyonnax to seal the last spot in the play-offs.
The European Champions Cup finalist ran in six tries, including a double from Juan Imhoff, and scored 21 unanswered points to pull away from the visitor, which had initially kept things tight.
Ole Avei, Manuel Carizza, Edwin Maka and So'otala Fa'aso'o also crossed for rampant Racing, with Benjamin Dambielle nailing every conversion as it joined Montpellier as confirmed participants in the last four.
Toulouse had been hoping to get into the top two, but it was beaten 36-26 by last season's champion Clermont Auvergne, which paid tribute to retiring captain Aurelien Rougerie with a guard of honour.
Castres came into its fixture in possession of the sixth and final play-off spot and made sure it held on to it with an emphatic 54-3 win over Oyonnax.
Five of the host's seven tries came inside the final 19 minutes, with Steve Mafi scoring twice as Castres booked a quarter-final contest against Toulouse.
The defeat means Oyonnax will contest the relegation play-offs and ensured Stade Francais avoids that fate despite losing 31-7 at La Rochelle, a result that was not enough to get the victor into the top six.
Lyon also made certain of its own progression to the play-offs, the fifth-place side beating leader Montpellier 32-24 after coming from behind with 10 points in the final nine minutes, Xavier Mignot's try clinching the victory.
It will meet Toulon, which suffered a 38-26 loss to Pau that was proved insufficient to keep the host's top-six aspirations alive.
Relegated Brive ended its stay in the top flight on a high, beating 14-man Bordeaux-Begles 22-20 courtesy of a penalty try after regulation time had expired.