Anthony Tuitavake was sent off as Racing 92 lost 23-19 at Agen in the Top 14.
Tuitavake was shown a straight red card for a dump takle on Julien Heriteau late in the first half. At that stage Racing were 7-3 ahead thanks to a try from Brice Dulin.
However, they found themselves behind at the break thanks to a converted score from Ricky Januarie, and Agen stretched their lead with a George Tinsley try.
Racing hit back with tries from Teddy Thomas and Bernard Le Roux but were unable to reel in their hosts, who had built a nine-point lead with seven minutes left thanks to the boot of Jake McIntyre.
Elsewhere, Stade Francais ran in five tries as they recorded a convincing win over La Rochelle at Stade Jean Bouin.
Stade were 30-7 in front at half time thanks to tries from Anoine Burban, Alexandre Flanquart, Sergio Parisse and Tony Ensor, two of which were converted by Jules Plisson who also added a pair of penalties.
Marvin O’Connor grabbed Stade’s fourth try before La Rochell — who had scored in the first half through Dany Priso — hit back through Afaesetiti Amosa and a penalty try. Ryan Lamb added a second-half penalty and conversion but it was never going to be enough to stop Stade.