Paris - South African scrum-half Rory Kockott, originally signed by Castres as emergency medical cover, kicked the French side to a 24-3 victory over champions Toulouse on Friday and top spot in the table.
The 25-year-old, who moved from South Africa's Sharks in the summer when Thierry Lacrampe was sidelined, kicked eight penalties and overshadowed Toulouse's former All Black Luke McAlister who endured an off-night with the boot.
McAlister was eventually taken off with Nicolas Bezy taking over the kicking duties, registering his team's only points with a penalty early in the second half.
The defeat was Toulouse's third in three years at Castres' Pierre-Antoine stadium.
"It was a very weak match by us," said Toulouse boss Guy Noves.
"We need to work on this failure. If we had scored our penalties we could have led 12-6. Not conceding a try is our only satisfaction."
Clermont moved into second place with a 29-13 victory over Agen with David Skrela marking his debut with 17 points.
Skrela, who left Toulouse in the summer, started in place of Australian fly-half Brock James.
It was his first match since a shoulder injury after just 11 minutes against Japan brought his World Cup to a painful, early finish last month.
Wesley Fofana and Jean-Marcellin Buttin were Clermont's try scorers.
Argentine international Juan-Martin Hernandez, who missed the World Cup because of a right knee injury, endured a miserable return to French Top 14 action when his Racing-Metro side slumped to a 22-18 loss at Bordeaux.
Hernandez had spent seven months on the sidelines, but was named in the starting line-up on Friday at full-back.
However, his return lasted only until the first minute of the second period when he was replaced by Verimi Vakatawa.
Fly-half Jonathan Wisniewski kicked all of Racing's points with his side 9-0 to the good at one stage before Bordeaux rallied with Julien Rey scoring the only try of the night just before the interval.
Five-time French champions Biarritz stay second from bottom after a 32-7 loss at Brive.