Toulon rose to the head of the Top 14 table with a 64-10 win over struggling Oyonnax on Saturday.
The leadership of the league became a dogfight with Clermont falling back to second on points difference after losing 26-16 to Bordeaux. Clermont led 13-9 at half-time, but were rocked by two tries from Fiji wing Metuisela Talebula.
Toulon went on a nine-try spree, with Drew Mitchell grabbing two and Jonny Wilkinson contributing 24 points with a try, eight conversions and a drop goal.
Castres fell back to sixth place after a shock 25-15 loss to Racing Métro. Rory Kockott contributed all Castres' points with five penalties, but he was eclipsed by Maxime Machenaud's five penalties and two tries by Argentinian wing Juan Imhoff.
Montpellier bounced back from last weekend's heavy defeat to Clermont with a 19-10 home win over Stade Français on Friday night, a result which saw the home side briefly leapfrog the Parisians into second place. They slipped back to third, three points behind, after Saturday's actions.
Montpellier came into the game on the back of a 42-16 thrashing last time out but were unable to make an early breakthrough in a scoreless first half, during which they were down to 13 men for 16 minutes as the sin bin filled up. But they burst into life after the break, taking the initiative with two quick-fire tries.
Bok flyhalf Morné Steyn contributed just one conversion and a penalty to Stade's score.
Toulouse also entered the play-off mix with a five-try win over Perpignan, which put them above Castres on a count-back with 55 points.
Montpellier 19 Stade Français 10
Bordeaux-Bègles 26 Clermont 16
Racing Métro 25 Castres 15
Brive 31 Grenoble 6
Toulon 64 Oyonnox 10
Toulouse 37 Perpignan 9
Biarritz 8 Bayonne 11
Photo: Martin Bureau/AFP Photo