Montpellier won 11-10 on home soil, Jan Serfontein’s try adding to a pair of Ruan Pienaar penalties, with Bordeaux left to count the cost of failing to convert either of Ed Fidow’s scores.
Charlie Slade impressed for Pau, booting 11 points, as they kept their noses ahead of Racing throughout.
Benjamin Urdapilleta kicked three penalties and converted veteran flanker Rodrigo Capo Ortega’s score as Castres took a 16-7 lead into the interval.
They were soon behind, though, as Toby Arnold crossed twice, but the reliable Urdapilleta split the posts again before adding the extras to tries from Armand Batlle and Julien Dumora to take the game away from Lyon.
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