A losing bonus point for Montpellier in Bayonne was enough to eliminate Perpignan from the race for the Top 14 play-offs on Saturday.
USAP were left empty-handed in Agen, meaning the Catalans are now seven points behind Montpellier and out of the running for the knock-out stages with one round of the regular season remaining.
In the late game, Grenoble fought back from 18 points down to claim a shock 25-24 victory over Toulon.
That results sees Toulon relinquish the championship lead to Clermont - who beat Toulouse earlier in the day - although the leading duo have both already qualified for the semi-finals.
Castres romped past Mont-de-Marsan to improve their chances of a home play-off while Biarritz slumped to defeat in Bordeaux.
SU Agen 23-15 USA Perpignan
Victory is too little, too late to save Agen from relegation but is certainly was enough to ruin Perpignan's domestic season.
Agen led from start to finish (10-5 at half time) for a deserved victory.
Aviron Bayonnais 32-26 Montpellier
It went right down to the wire in the Basque country, where the scored were locked at 26-all going into the final ten minutes.
Two late Jacques-Louis Potgeiter penalties handed the hosts the win that sees them rocket up to ninth in the standings, a point above local rivals Biarritz.
A losing bonus point is just reward for a Montpellier side that fought back valiantly after trailing 23-12 with half an hour to play.
Bayonne led 17-12 at the break thanks to a controversial penalty try after Montpellier scrum-half Benoit Paillaugue was sent to the been for intentionally knocking the ball over the dead-ball line.
Union Bordeaux-Bègles 16-0 Biarritz Olympique
UBB continued their strong late season form against a below-strength, and under-motivated Biarritz side.
A place in the top ten is now within reach of Bordeaux while BO are focussed on retaining their Challenge Cup title.
Castres Olympique 44-17 Stade Montois
Castres will now anxiously await the result of Sunday's Paris derby to know what they need from their clash against Racing on the final day to claim a home play-off.
CO are now just one point behind third-placed Toulouse.