La Rochelle defeated Lyon 19-15 away from home on Saturday to move within three points of the Top 14 leaders, as Racing 92 and Toulouse also won.
Brock James kicked four penalties and converted Alexi Bales' second-half try to make the difference at Stade de Gerland, where Frederic Michalak sent over five penalties for the try-less hosts.
Lyon remain in first place despite losing in the Top 14 for the first time since September.
Toulouse, meanwhile, are fourth, two points behind second-placed La Rochelle, after snatching a 38-37 victory over Bordeaux Begles.
The away team had led 34-24 at the break after running in four tries in the space of 14 first-half minutes, but Joe Tekori's converted try in the 75th minute was enough for Toulouse to deny the visitors at Stade Ernest-Wallon.
Racing 92 are four points further back from Toulouse in sixth spot after leaving it even later at home to Pau, Pat Lambie converting Marc Andreu's try with just a minute left to secure a 23-20 triumph.
Castres were more comfortable in beating Oyonnax 32-19 on the road, while a dramatic late penalty helped struggling Agen to upset Toulon 26-24 at home and record just their second victory of the season.