Clermont inflicted a 40-17 defeat on Racing 92 in the Top 14 on Sunday, handing the big-money club their first defeat at their new home in Paris' La Defense business district.
Racing boasted the best defence in the league last season but they were undone again and again by the 2017 champions, fired by Greig Laidlaw's kicking, as they were beaten at the Arena for the first time since taking up residence in December last year.
Scotland scrum-half Laidlaw, watched by his national coach Gregor Townsend, was successful with five of six penalties and Wesley Fofana, New Zealander Peter Betham and Damian Penaud all scored tries.
Tries by Virimi Vakatawa and new signing Simon Zebo, the Ireland international, were in vain for the home side.
Clermont's sporting director Franck Azema said despite two wins out of two to open the season, the team was still building its confidence after a poor 2017-2018 campaign.
"We're not going to get carried away, we're not in that frame of mind. We're coming off a very difficult season so that's in the front of our minds," Azema said.
In Sunday's other match in France, Agen put their backroom worries and a painful opening day thumping behind them when they edged promoted Perpignan 25-23 in an encounter between two sides tipped for relegation.
Agen took a hiding going down 67-23 at Clermont last weekend and then announced midweek that their inspirational coach Mauricio Reggiardo would be moving on to Castres as manager next season.
Reggiardo's charges quickly racked up three tries Sunday with two from Jake McIntyre either side of Sam Vaka's effort.
But they were pegged back as Perpignan, who lost 46-15 to Stade Francais last week, rallied in a no-holds-barred bid for the points after Enzo Selponi got their second try on 68 minutes.
"We needed this win. That was a really high pressure match. Those four points will give us a bit of peace of mind this week," said Reggiardo.
"But we have work to do, that was not a mature performance and we failed to respect our opponents at a key moment of the game," he said.
Toulon gave debuts to their two All Black recruits on Saturday but still lost for the second time in the French Top 14 this season, beaten 20-10 at Pau.
Reigning champions Castres battled back to beat Lyon 19-16 and ambitious Stade Francais also made it two wins from two by seeing off Bordeaux-Begles 20-8.