Racing Metro all but booked their place in the Top 14 play-offs and condemned Stade Francais to missing out with a 19-13 victory over their bitter rivals at Stade de France on Saturday.
Victory gives Racing a five-point advantage over Stade with a game remaining and leaves the latter needing to beat Biarritz away with a bonus point and for Racing to fail to pick up a bonus point in their trip to Agen to make the play-offs.
It is likely to mean that the 13-time French champions - five of their wins coming in the past 14 years - miss out on the play-offs for the third successive year.
It would leave Stade hoping Toulon beat Biarritz in the European Challenge Cup final later this month so they could at least have the consolation of qualifying for next season's European Cup.
Toulon had earlier ensured their qualification for the play-offs, while Brive plunged towards the second relegation spot after losing to Bordeaux-Begles.
Toulon enjoyed a three-tries-to-one 25-22 victory over Toulouse, who are already through to the semifinals of the end-of-season finale with Clermont as the two top finishers.
"Even if we weren't outstanding in the past month, we are confident we have the weaponry required for the play-offs," said Toulon forwards coach Olivier Azam.
Toulon's win saw them move into third spot, with Montpellier also having qualified for the six-team play-offs by beating Biarritz 21-16 on Friday.
Castres beat Clermont 30-19 to also qualify for the play-offs.
At the other end of the table, Bayonne took a massive step towards survival in the Top 14 with a bonus-point 31-10 home win over Agen.
But there were tears as Brive's 23-9 loss at home to Bordeaux left the latter safe but the hosts in 13th place, five points adrift of Bayonne.
Brive now face the prospect of not only having to win with a bonus point in their final away game at heavyweights Clermont, but also need Bayonne to lose, without picking up a defensive bonus point, away to Castres.
Lyon, beaten 34-22 by Perpignan, sit bottom of the table and their relegation to the Pro D2 has already been confirmed.
In a strangely muted Stade de France, Stade Francais surged into a 10-0 lead mid-way through the first-half, with Julien Arias touching down after a well worked move down the left flank involving Dimitri Szarzewski and Felipe Contepomi.
Julien Dupuy, who had earlier slotted over a penalty, converted.
Racing flyhalf Jonathan Wisniewski kicked two penalties to put them in touch and shortly before half-time they went ahead for the first time, taking advantage of Argentinian veteran Felipe Contepomi being sin-binned.
Stade appeared to have snuffed out a Racing attack down the right wing but instead of putting the ball in touch they handed possession back to their opponents and a nice break by Juan-Jose Imhoff carved open the Stade defence.
He offloaded to Sebastien Descons, who ran it in under the posts and Wisniewski converted for a 13-10 scoreline at the break.
Wisniewski added another penalty in the 58th minute for 16-10 before Dupuy reduced the deficit to three points again with a penalty of his own with less than 20 minutes remaining.
Wisniewski slotted another penalty with 10 minutes to play and although Stade mounted a late rally and pressured the Racing try line, they could not break through the defence.
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