Newly promoted Bayonne celebrated an opening-day upset as the new Top 14 season began on Saturday, winning 24-17 away at Racing 92.
Bayonne won the Rugby Pro D2 title last season to seal their return to the top flight and used that momentum to spring a surprise as they visited Racing in the first round of fixtures.
The visitors trailed 17-7 at half-time after Michael Ruru's try only briefly cancelled out a Racing lead that was forged by Yoan Tanga Mangene and restored by Juan Imhoff.
But after Teddy Iribaren's penalty on the stroke of half-time, Racing did not score again.
Romain Barthelemy kicked four second-half penalties of his own, while Aymeric Luc added a second Bayonne try, as Racing's ill discipline cost them, with Tanga Mangene and Hassane Kolingar each yellow-carded.
Fellow promoted side Brive had a less successful return to the big time as they lost 33-14 at Pau, despite seeing the hosts reduced to 14 men after just 20 minutes.
Pau led 7-0 at the time of Matthieu Ugena's dismissal and managed to stretch their advantage to 23-14 before Brive themselves had a man, Joris Jurand, see red, with the home side then running in two late tries.
Elsewhere, champions Toulouse were beaten in the first match of their title defence, going down 30-25 at Bordeaux-Begles.
The sides shared five tries, eight penalties and three yellow cards, with Matthieu Jalibert decisively crossing moments after Selevasio Tolofua's 65th-minute sin-binning.
Lyon thrashed Stade Francais 43-9 for a bonus point, which Toulon also claimed as they triumphed 44-25 at Agen.
Castres and Montpellier were separated by just two points either side of the play-off line last season and the former, losers on that occasion, edged victory by a point on Saturday.