Jonathan Sexton kicked six from six as Racing Metro marked their first home game at Stade Yves Du Manoir with a hard-earned 22-9 win over promoted Oyonnax.
Sexton hit five penalties and a conversion as they finally got on top of an Oyonnax side where former Leinster team-mate Damian Browne made his debut.
Oyonnax, the club with the smallest budget in the Top 14 but who had stunned Clermont the previous week, led 9-6 at the break but three yellow cards and the unerring boot of Sexton saw Racing Metro home, with a try from hooker Virgile Lacombe denying the promoted side a bonus point.
The club with the biggest Irish contingent in France ended the last unbeaten record after just three rounds as Grenoble, with former Irish hooker Bernard Jackman and ex-Munster scumhalf Mike Prendergast on the coaching ticket, held out 28-26 to Toulon.
“It was a huge win for us . . . and it was really important for us to follow up our opening day win over Stade Francais with another victory,” said Jackman, whose side were promoted last year.
Stade Francais are the new leaders of the Top 14 following a 38-3 drubbing of Biarritz as 20,000 turned out for the first game in their €150 million Stade Jean Bouin.
Clermont Auvergne made it 60 games unbeaten at home when they hammered Toulouse 38-19, while Montpellier became the final side this campaign to win a game when they held on to beat Brive 33-24.
Champions Castres lost their second game 21-20 away to Bordeaux-Begles, while Perpignan lost a second in a row when going down 31-20 at Bayonne.
In the Pro D2, which started this weekend, former Munster hooker Denis Fogarty made a winning start to his career with Agen when they won 17-12 at Albi, but former Irish international Jeremy Davidson saw his Aurillac side beaten 34-23 at Narbonne, with ex-Ulster hooker Nigel Brady making his debut off the bench for the visitors. Brian Hayes, who has joined Aurillac from Munster, and Conor Gaston were not in the squad but Mark Flanagan made his debut in the second row for Mont de Marsan against La Rochelle .