In-form Racing 92 replaced La Rochelle in second spot in the Top 14 with a 19-12 victory, while Castres edged out Bordeaux-Begles on Sunday.
Racing continued their charge at the U Arena, their new home, securing an eighth win in a row to move above their opponents in the table.
The Paris club bossed the first half, scoring all 19 of their points without reply, with Yannick Nyanga, Juan Imhoff and Pat Lambie going over as La Rochelle struggled to make their presence felt.
Afa Amosa powered his way over to get La Rochelle on the board nine minutes into the second half and Paul Jordaan crossed late on, but the away side were unable to prevent Racing from moving only two points behind leaders Montpellier.
Julien Dumora's first-half try was decisive at Stade Chaban-Delmas, where Castres beat Bordeaux 7-6.
Castres were in need of a win after back-to-back Top 14 defeats and Dumora touched down after racing onto a kick from Benjamin Urdapilleta, who converted to give the visitors a 7-3 lead.
Baptiste Serin's second penalty of the game reduced the deficit, but Bordeaux were unable to turn it around.