Toulouse thrashed Toulon 31-8 to move to the summit of the Top 14 table on Sunday after Racing 92 beat previous leaders Clermont Auvergne 20-16.
European champions Toulon would have felt they had a score to settle after Toulouse did the double over them last season, but they were swept aside at Stadium Municipal.
Gael Fickou scored the only try of the first half as the hosts went into the break with their noses in front at 10-3 and they shifted through the gears after the interval.
Maxime Medard, Yacouba Camara and Dorian Aldegheri added further tries in a one-sided second half, ensuring Toulouse lead Racing and Clermont by three points and Toulon are down in fifth.
Racing won at Stade Marcel Michelin for the first time in 21 years to take over at the top for a short while until Toulouse dislodged them.
Three Morgan Parra penalties put Clermont 9-6 at the end of a first half in which Racing lost Louis Dupichot to the sin bin late on.
The visitors then took hold of the game and were rewarded with tries from Johan Goosen and Henry Chavancy, with Fritz Lee's converted try no more than a consolation for Racing as they suffered only their second Top 14 defeat of the season.
Oyannax moved off the bottom of the table by beating struggling champions Stade Francais 25-12, with the only try scored by Jimmy Yobo early in the second half.
Agen are now bottom after they were hammered 45-20 at Montpellier, while Conrad Smith's Pau debut ended in a much-needed 15-11 win over La Rochelle.
Bordeaux Begles sit fourth courtesy of a 25-19 win over Grenoble, and Castres were 23-8 winners over Brive.