Leader Clermont was in action along with the rest of its rivals, taking advantage of Stade's moved fixture with a 28-8 success over Toulon.
Damian Penaud, Camille Lopez, Remy Grosso and Yohan Beheregaray all crossed to send Franck Azema's team six points clear.
Champion Castres moved level with Stade on 18 points after Alex Tulou's two second-half tries turned a clash with Toulouse in the visitor's favour.
Montpellier was also a narrow winner as Perpignan suffered a sixth straight defeat to start the season, with a last-gasp fightback unable to prevent a 23-20 triumph for Vern Cotter's side.
Fourth-placed Lyon saw off Grenoble 34-6 as Noa Nakaitaci touched down twice, while Bordeaux-Begles scored all of their 34 points in the first half to defeat La Rochelle 34-22.
Antoine Hastoy was Pau's match-winner as he scored 23 of its points, including two tries, in a tense 28-25 victory at Agen.