Racing 92 fell to a surprise defeat at Pau to fall six points behind Montpellier, which narrowly beat Bordeaux to pull clear at the Top 14 summit.

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 it kept its noses ahead of Racing throughout.

Watisoni Votu scored a second-half double to help Pau move level on points with Toulon and Toulouse in the final play-off spots, ahead of those sides' assignments on Monday (AEDT).

Racing's reverse snapped an eight-game winning run across all competitions and Castres is now just three points behind on the table after beating Lyon 33-22.

Benjamin Urdapilleta kicked three penalties and converted veteran flanker Rodrigo Capo Ortega's score as Castres took a 16-7 lead into the interval. 

it was soon behind, however, 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.

Agen climbed out of the bottom two by beating Stade Francais 36-34 in a thriller, while rock-bottom Oyonnax beat Clermont 18-12, just its second win of the season.