La Rochelle will start 2018 as the Top 14 leaders following a 47-6 demolition of Agen, as Montpellier were beaten at lowly Brive on Saturday.
Back-to-back defeats against Wasps and Bordeaux-Begles - the former in European competition - had rocked La Rochelle in recent weeks, but they got back on track with a seven-try rout at Stade Marcel Deflandre.
Jeremy Sinzelle, Pierre Bourgarit and Alexi Bales scored first-half tries for the home side, who led 21-6 at half-time as struggling Agen could only muster two Hugo Verdu penalties.
La Rochelle dominated the second half as well, with Gregory Lamboley going over just after the interval. Pierre Aguillon, Afaesetiti Amosa and Pierre Boudehent added further tries and Ryan Lamb scored 12 points with the boot as the new table-toppers finished 2017 with a flourish.
Montpellier's three-game winning streak was halted at Stade Amedee-Domenech, where Brive produced an upset by winning 29-10.
Brive had lost three in a row and only had three wins to their name prior to this in the French top flight all season, but they scored 22 points without reply in the second half to knock Vern Cotter's big spenders off the summit.
Nadir Megdoud scored two tries in the space of three second-half minutes after a converted Benjamin Fall try had edged Montpellier in front at 10-7.
Benjamin Lapeyre added a third five-pointer 11 minutes from time to give Brive breathing space and there was no way back for Montpellier.
Racing 92 sit third after they were 16-12 victors at bottom side Oyonnax, Toulouse leapfrogged Toulon into fifth with an 18-13 win over the three-time European champions, and Stade Francais beat Bordeaux-Begles 22-12.