Toulon have moved provisionally into fourth position in the standings after beating Top 14 champions Castres 19-13 at Stade Felix Mayol on Saturday.
With Clermont having lost 16-13 at Grenoble on Friday, the race to finish at the regular-season summit has intensified over this latest round.
Toulon move on to 51 points, level with Castres and four behind Les Jaunards, with the second-placed Stade Franšais tackling Brive later today.
Three penalties from fly-half Jonny Wilkinson - in the tenth, thirteenth and thirtieth minute - put the hosts 9-0 ahead going into the half-time break.
However, the second-half was more entertaining as Max Evans' score that was converted by Rory Kockott made it 9-7 with seventeen minutes left.
Toulon though would regroup and scored a try of their own soon after, with Matt Giteau going over before Wilkinson added the extra two points and another penalty goal on 74 minutes that took Castres out of losing bonus-point range.
Kockott, however, would reply before the end to salvage a point for his side, who host Toulouse next week while Toulon travel to Bayonne in the lone Sunday fixture.
Pen: Wilkinson 4
Pen: Kockott 2
Toulon: 15 Delon Armitage, 14 Drew Mitchell, 13 Maxime Mermoz, 12 Matt Giteau, 11 David Smith, 10 Jonny Wilkinson, 9 Frederic Michalak, 8 Steffon Armitage, 7 Virgile Bruni, 6 Juan Smith, 5 Ali Williams, 4 Jocelino Suta, 3 Levan Chilachava, 2 Craig Burden, 1 Emmanuel Felsina.
Replacements: 16 Benjamin Noirot, 17 Xavier Chiocci, 18 Danie Rossouw, 19 Pierrick Gunther, 20 Mathieu Bastareaud, 21 Rudi Wulf, 22 Michael Claassens, 23 Martin Castrogiovanni.
Castres: 15 Geoffrey Palis, 14 Max Evans, 13 Romain Cabannes, 12 Seremaia Bai, 11 Remy Grosso, 10 Remi Tales, 9 Rory Kockott, 8 Antonie Claassen, 7 Jan Bornman, 6 Ibrahim Diarra, 5 Richie Gray, 4 Christophe Samson, 3 Karena Wihongi, 2 Brice Mach, 1 Yannick Forestier.
Replacements: 16 Marc Rallier, 17 Saimone Taumoepeau, 18 Rodrigo Capo Ortega, 19 Pedrie Wannenburg, 20 Julien Tomas, 21 Daniel Kirkpatrick, 22 Marcel Garvey, 23 Anton Peikrishvili.
Referee: Romain Poite