All Black sees red as Racing suffer against Agen
Elsewhere, Louis Picamoles marked his Montpellier return with a try as Oyonnax were beaten 37-6.
Racing were made to pay for a moment of madness by All Black centre Anthony Tuitavake, who upended Julien Heriteau in the 39th minute.
Agen's former Reds playmaker Jake McIntyre broke the deadlock of a tight opening with a penalty before Racing fullback Brice Dulin crossed for the first try of a mistake-ridden match with Agen's Ricky Januarie in the sin-bin.
From a scrum deep in Agen territory, France international Dulin made the numerical advantage pay as he received the ball at pace and scooted past a stretched defence for a five-pointer All Black legend Dan Carter converted.
But Racing were then guilty of spurning a handful of opportunities in their bid to force the final pass, Agen doing just enough to stay in the game.
Racing were dealt a hammer blow just before half-time when Tuitavake, a six-time capped All Black, was shown a direct red card for a nasty-looking tip tackle on opposite number Heriteau.
"The red card for Tuitavake was fair," said Racing backs coach Laurent Labit.
"It penalised us, but we had to do the work before that. We can find some excuses with the return of the internationals, but it will take us weeks to get it right.
"Without disrespecting Agen, we had the means to win this match,"
From the resulting penalty and pressure from the home side, Januarie, 47 times a Springbok, showed all his experience with a feint to cross from short range, McIntyre converting to hand Agen a 10-7 half-time lead.
The Australian flyhalf extended Agen's lead with a penalty early in the second half and then converted a touchline try from George Tilsley, the former New Zealand 7s player benefitting from a smart break and pass by Heriteau.
Racing gave themselves a lifeline by immediately responding with a Teddy Thomas try converted by Carter.
Racing's replacement scrumhalf Maxime Machenaud thought he had skipped over for the Paris side's second try under the posts, but Bernard Le Roux was penalised for holding back Baptiste Serin.
Instead McIntyre banged over a third penalty, but Racing at least headed home having bagged a defensive bonus point after Le Roux was driven over for his team's third try from close range late on, Carter converting.
Later on Saturday, Montpellier and Lyon both made it back-to-back wins to start the campaign.
French international number eight Picamoles made his first appearance for Montpellier in eight years after his move from English Premiership outfit Northampton.
Hosts Montpellier totally dominated Oyonnax, with Picamoles crossing for their fifth and final try seven minutes from time.
Vern Cotter's side now lead Lyon by two points at the top of the early table after two bonus-point victories.
"There is work to be done to get to the level we want, even if our state of mind and defence have been OK," said Picamoles.
"We will have to quickly improve our level of play and cut out the indiscipline and slackness in our game."
Lyon overcame an indifferent first-half display to see off Brive 29-14, while talismanic Italian Sergio Parisse scored a try as Stade Francais claimed their first win of the season by beating La Rochelle 35-24 in Paris.
Bordeaux-Begles were brought back down to earth after their stunning win over Clermont last week with a 33-19 loss at Castres, and Toulouse claimed their first win by holding off Pau 23-19.
Reigning champions Clermont will look to bounce back when they host Toulon on Sunday in a repeat of last season's final.
Top 14 results:
Agen 23 Racing 19
Stade Francais 35 La Rochelle 24
Castres 33 Bordeaux-Begles 19
Lyon 29 Brive 14
Montpellier 37 Oyonnax 6
Toulouse 23 Pau 19
Fixture:
Sunday
Clermont v Toulon (14.50 GMT)
Agence France-Presse
