Toulon ran in six tries as they routed Biarritz 50-15 at Stade Mayol. Bakkies Botha ran in an early try for the hosts, only for Benôit Baby to reply quickly for Biarritz.
However it was a temporary fight from the visitors as Alexis Palisson, Matt Giteau, Nick Kennedy, Rudi Wulf and Sebastian Bruno all scored for the leaders, while former England fly-half Jonny Wilkinson added 22 points with the boot.
Clermont ran out 37-10 victors over Castres at their Stade Marcel Michelin home, with Sitiveni Sivivatu, Gerard Vosloo, Napolini Nalaga and a penalty try ensuring they kept pace at the top.
Castres are fourth, but now 16 points behind Clermont.
Third-placed Toulouse snatched the narrowest of victories over Bordeaux, 33-32 at Stade Toulousain.
France international Lionel Beauxis sent over a 68th-minute penalty to seal the win, but Nicolas Sanchez’s drop-goal attempt came close to winning it for Bordeaux.
Stade Français easily beat struggling Mont-de-Marsan 42-14, Bayonne won 30-20 at Agen and Perpignan were 20-18 winners at home to Grenoble.