Top 14 leaders Toulon suffered just their sixth defeat of the season on Saturday, going down 33-28 to Bayonne at the Estadio de Anoeta in Saint Sebastian.
Bayonne, who started the weekend in eleventh place in the standings and were thrashed 59-0 in Toulon earlier this season, led 20-11 at the break.
The below-full-strength visiting side, that featured ex-Springbok Danie Rossouw making his debut in the back row, fought back in the second half but had to settle for a losing bonus point.
Toulon, mindful of their Heineken Cup quarter-final against Leicester in a fortnight, left out the likes of Jonny Wilkinson and Matt Giteau while Frederic Michalak was sidelined with a shoulder injury suffered in the Six Nations.
Despite the defeat, long-time leaders Toulon still managed to carve out a losing bonus point, scoring three tries through Jean-Charles Orioli, Joe van Niekerk and Sebastien Tillous-Borde.
Scott Spedding, Marvin O'Connor and South African Sam Gerber, a 10th-minute replacement for winger Bastien Fuster who was taken off after a nasty clash with Toulon full-back Delon Armitage, scored tries for Bayonne.
The match was a sobering experience for Benjamin Lapeyre who was handed the task of replacing Wilkinson at fly-half and was, by his own admission, found wanting at crucial moments.
"I missed a try and some other opportunities, but some of the guys haven't had a lot of playing time," said Lapeyre, whose career has largely been spent at full-back, on the wing or in the centres.
"It's been three or four years since I played at fly-half. Everyone helped me and I have to thank the forwards. Sometimes I was a little lost but I was quick when it came to fixing my errors.
"I did some good things and some bad things, but I don't think I am going to take Jonny's place."
Tries: Spedding, O'Connor, Gerber
Cons: Potgeiter 3
Pens: Potgeiter 4
Yellow card: Spedding
Tries: Orioli, Van Niekerk,Tillous-Borde
Cons: Palisson 2
Pens: Armitage 2, Palisson
Bayonne: 15 Scott Spedding, 14 Bastien Fuster, 13 Joe Rokocoko, 12 Thibault Lacroix, 11 Marvin O'Connor, 10 Jacques louis Potgeiter, 9 Guillaume Rouet, 8 Dwayne Haare, 7 Julien Puricelli, 6 Mark david Chisholm, 5 Dewald Senekal, 4 Abdellatif Boutaty, 3 Renaud Boyoud, 2 David Roumieu, 1 Aretz Iguiniz,
Replacements: 16 Gregory Arganese, 17 Pierre Lafond, 18 Marc Baget rabarou, 19 Guillaume Bernad, 20 William michael Phillips, 21 Matthieu Ugalde, 22 Sam Gerber, 23 Vitolio Manukula.
Toulon: 15 Delon Armitage, 14 David Smith, 13 Geoffroy Messina, 12 Maxime Mermoz, 11 Vincent Martin, 10 Benjamin Lapeyre, 9 Sebastien Tillous borde, 8 Danie Rossouw, 7 Pierrick Gunther, 6 Joe van niekerk, 5 Jocelino Suta, 4 Simon Shaw, 3 Levan Chilachava, 2 Jean Charles Orioli, 1 Gethin Jenkins,
Replacements: 16 Mickael Ivaldi, 17 Xavier Chiocci, 18 Konstantine Mikautadze, 19 Virgile Bruni, 20 Alexis Palisson, 21 Ivan Roux, 22 Nicolas Durand, 23 Davit Kubriashvili,