Montpellier scored a 22-11 victory that kept the heat on the Top 14 leading four while also compounding USAP's woes at the foot of the table on Friday.
The win leaves Montpol in fourth spot and they'll remain there for another week at least due to Saturday's Agen v Castres game being called off.
Perpignan meanwhile remain eleventh and just four points off bottom spot as home tries from Alex Tulou, Lucas Amorosino and Mamuka Gorgodze more than cancelled out Rudi Coetzee's lone five-pointer from the visitors.
Tries: Tulou, Amorosino, Gorgodze
Con: Fernandez, Bustos-Moyano
Pen: Porical 2
Biarritz 15-20 Toulouse
Toulouse extended their lead at the Top 14 summit to ten points as they beat Biarritz.
France's league leaders had gained a 17-3 lead just after the half-hour thanks to scores from scrum-half Luke Burgess and wing duo Timoci Matanavou and Yves Donguy.
Benoit Baby's penalties and a drop from Damien Traille brought BO back into it though.
But despite being reduced to 13 men after two yellow cards the visitors held on for another win that adds further worry to struggling Biarritz's future.
Pen: Baby 4
Tries: Burgess, Matanavou, Donguy