Juan Imhoff scored a second-half double as Racing 92 hammered Pau 31-3 and Toulon beat La Rochelle in the Top 14 on Sunday.
Pau could have returned to third spot with a victory at Stade du Hameau, but Racing dominated the second half to claimed only their second win of the season.
Two Teddy Iribaren penalties either side of one from Colin Slade gave Racing a 6-3 half-time advantage and the capital club took charge after the break.
Iribaren doubled his tally from the tee before the clinical Imhoff, overlooked by Argentina coach Mario Ledesma for the Rugby World Cup, touched down twice in the space of 12 minutes.
Replacement scrum-half Sam Hidalgo-Clyne added a third try right at the end to cap a miserable afternoon for Pau.
La Rochelle were unable to show a positive response to their defeat to Bayonne, going down 23-3 at Toulon.
Facundo Isa and Julian Savea scored second-half tries at Stade Mayol, with Anthony Belleau notching 11 points with the boot as Toulon moved up to seventh spot.