Clermont Auvergne claimed their third bonus-point victory on the bounce as they triumphed 41-24 at Oyonnax on Saturday.
Last season's runners-up have made the perfect start to their season and ran in five tries to open up a three-point lead at the summit.
Nicky Robinson initially kept Oyonnax competitive with the boot, but three first-half tries saw Clermont lead 24-12 at half-time.
Adrien Plante met a Camille Lopez cross-field kick to touch down in the corner just short of the hour mark as the visitors stretched their lead further with Oyonnax down to 14, before two tries from hooker Jerome Marouard helped reduce the deficit.
Fritz Lee had been sent to the sin bin prior to the hosts' double, but Clermont recovered to wrap up the bonus point with a late Alivereti Raka try.
Toulouse kept up their early challenge with a convincing 37-20 victory over Castres, while third-place Grenoble were even more emphatic in their 41-15 demolition of Pau.
Grenoble lost to Clermont last weekend but two tries from number eight Rory Grice helped get them back on track.
That victory saw Grenoble climb above Racing 92, who suffered their first defeat of the season, losing 30-18 at newly promoted Agen.
In the day's remaining clash, La Rochelle beat Brive 21-18 for their first win of the of the new campaign.
