Toulon slipped to a surprise defeat at La Rochelle in Top 14 on Sunday as a try from Pierre Aguillon and the boot of Zack Holmes earned the home side a 19-14 success.
The three-time defending European champions had seen title rivals Racing 92 and Clermont Auvergne both win earlier in the weekend, but knew victory would see them return to the summit.
In a bruising encounter, the key score came courtesy of Aguillon with 10 minutes to go as La Rochelle moved up a place to ninth, with Tom Taylor's try right at the end ensuring Toulon picked up a losing bonus point.
Toulon led 6-3 at the break thanks to two Jonathan Pelissie penalties, while both sides had been reduced to 14 men after an altercation between Drew Mitchell and Levani Botia.
Two successful kicks from Holmes had La Rochelle in front before Pelissie brought Toulon level, and Botia found himself in the wars again when he was briefly knocked unconscious after a thunderous collision with Mathieu Bastareaud.
With the game finely poised, Aguillon held off the attentions of a couple of defenders to touch down and, after Holmes took his tally to 14 points, Taylor's try with the clock already past 80 minutes earned a consolation point for the visitors.