Toulon took a step closer to an automatic Top 14 semi-final spot on Saturday with a 37-21 win over Castres at Stade Felix Mayol.
The triple European champions outscored their visitors five tries to three, meaning the miss out on a try bonus point.
Toulon cruised to a 23-7 by half time thanks to tries from flank Steffon Armitage, prop Xavier Chiocci and wing Josua Tuisova while Castres replied via a try from wing Romain Marital.
Tuisova bagged his second try shortly after the break before full-back Leigh Halfpenny crossed for Toulon's fifth try to put the result beyond any doubt.
But Castres didn't go down quietly and late tries from replacement scrum-half Rory Kockott and centre Romain Cabannes denied Toulon the bonus point that would have moved them out of Clermont's reach in the standings.
Toulon had started strongly against an understrength Castres side, with Armitage giving them the lead after just 11 minutes following a powerful burst by Chris Masoe. Mathieu Bastareaud delivered the final pass for his flanker, with Halfpenny missing the conversion but making up for it a few minutes later with a penalty.
Castres responded with a try from nowhere, as Tuisova failed to deal with a kick over the top by Julien Dumora, and Martial was on hand to sprint over. With Dumora's conversion Castres trailed by just a point midway through the half, but Toulon hit back straightaway.
It wasn't complicated stuff from the champions, as Chiocci took advantage of an unclaimed restart to collect the ball and sprint 30 metres to power over. Again Halfpenny was off-target with the conversion, somehow missing from in front of the posts.
The Welshman knocked over his second penalty of the afternoon on the half-hour, before Tuisova scored his first try after a lovely move from the home side. Matt Giteau started it as he put Halfpenny through a gap, and the full-back sprinted away before feeding Tuisova. The Fijian showed his finishing skills as he beat three men to dot down.
With Halfpenny's conversion Toulon led 23-7 at the break, and Tuisova grabbed his second early in the second half as Toulon took advantage of a long passage of play to open up space on the left, with Armitage delivering the final pass for the Fijian to sprint over.
On the hour Halfpenny extended the lead to 37-7, as he was on the end of Drew Mitchell's grubber that had cruelly bounced away from both Rémi Lamerat and David Smith.
With a four-try advantage, Toulon looked home and dry in the race for a bonus point, but that wasn't the case as Castres introduced some of their bigger names in the closing stages, with Kockott diving over from close range.
There was still time for one more try, Cabannes this time finishing despite the attentions of Giteau coming back in defence. Toulon had to settle for four points as a result, but with an eight-point gap back to Clermont at the top of the table, they look well-placed to finish top of the pile.
Tries: Armitage, Chiocci, Tuisova 2, Halfpenny
Cons: Halfpenny 3
Pens: Halfpenny 2
Tries: Martial, Kockott, Cabannes
Cons: Dumora 3
Toulon: 15 Leigh Halfpenny, 14 Drew Mitchell, 13 Mathieu Bastareaud, 12 Rudi Wulf, 11 Josua Tuisova, 10 Matt Giteau, 9 Sébastian Tillous-Borde, 8 Chris Masoe, 7 Steffon Armitage, 6 Juan Martín Fernandez Lobbe, 5 Ali Williams, 4 Bakkies Botha, 3 Carl Hayman, 2 Guihelm Guirado, 1 Xavier Chiocci
Replacements: 16 Jean-Charles Orioli, 17 Alexandre Menini, 18 Romain Taofifeuna, 19 Virgile Bruni, 20 David Smith, 21 Frédéric Michalak, 22 Eric Escande, 23 Martin Castrogiovanni
Castres: 15 Julien Dumora, 14 Romain Marital, 13 Thomas Combezou, 12 Romain Cabannes, 11 Marcel Garvey, 10 Daniel Kirkpatrick, 9 Cedric Garcia, 8 Jannie Bornman, 7 Mathieu Babillot, 6 Ibrahim Diarra, 5 Benjamin Desroches, 4 Christophe Samson, 3 Ramiro Herrera, 2 Mathieu Bonnello, 1 Mathieu Bonnello
Replacements: 16 Marc-Antoine Rallier, 17 Yannick Forestier, 18 Rodrigo Capo Ortega, 19 Johnnie Beattie, 20 Rory Kockott, 21 Rémi Lamerat, 22 Geoffrey Palis, 23 Paea Fa'anunu
Referee: Mathieu Raynal