Fly-half Antoine Hastoy made the difference with his boot as La Rochelle survived a late Lyon fightback to edge their Top 14 rivals 23-21 in their first away game this season but Paris clubs Racing 92 and Stade Francais both suffered defeats on the road.
European champions La Rochelle remained unchanged from the starting XV that opened their campaign with a win against French champions Montpellier at home last weekend.
But after dominating for nearly an hour and touching down twice, La Rochelle endured a nervy finish with Lyon scoring three tries to earn a bonus defensive point.
La Rochelle take top spot in the Top 14 table after their second win Montpellier hosting Bordeaux Begles later Saturday and Toulouse playing Toulon on Sunday.
Racing 92 threw away a 10-point lead at the break to fall 31-25 at promoted Bayonne who like Castres got their first win of the season 30-20 at home against Stade Francais.
A well-structured gameplan and their opponent's shortcomings had allowed La Rochelle take control in Lyon. New Zealand scrum-half Tawera Kerr-Barlow touched down their first try after 12 minutes.
Hastoy punished the opposition with two penalities as the visitors surged to a 13-0 lead after 43 minutes. The 25-year-old France international kicked 13 points to ensure victory even though Lyon scored one more try.
Lyon dug deep with Georgian Davit Niniashvili touching down the first of his side's tries after 57 minutes.
La Rochelle's South African winger Dillyn Leyds responded with a second try for his side, before late tries from international scrum half Baptiste Couilloud and New Zealand centre Josiah Maraku ensured a tense finish.
"The last five minutes were very stressful," said La Rochelle full back Brice Dulin.
"Lyon played their luck to the full and it almost cost us dearly. We have to be able to kill games and not let the opponents come back.
"The last ten minutes left a bitter taste. We are aware that we could have lost it."
Castres bounced back for last week's defeat at Racing 92, with a three-try win over Stade Francais.
Tries from Geoffrey Palis and Fijian pair Adrea Cocagi and Vilimoni Botitu put Castres on their way with a 30-10 half-time lead.
Stade Français attacked in the second half and were rewarded with a try from winger Sefanaia Naivalu after 46 minutes, the second for the team after Nemo Roelofse's in the first half.
Despite being increasingly dangerous, the Parisians were unable to made the difference allowing Castres increase their unbeaten home run to 22 matches.
"We lacked control, made a series of mistakes in the first half," lamented Stade manager Gonzalo Quesada.
"Castres showed realism, were pragmatic on all their balls. We will remember the second half. A another time, we would have taken 45 points. There is work, but there are also good things".
Racing 92, led by ten points at the break, only to crack at Bayonne who bounced back after last week's loss to Toulon.
The Paris side were 18-8 at the break, after Enzo Benmegal and Finn Russell scored two tries and thanks to the boot of Nolann Le Garrec.
Facundo Boschgot had scored a try after six minutes for Bayonne with Thomas Ceyte and Teiva Jacquelain touching down two more in a three-minute second half spell to revive the Basque side.
"We were present for 40 minutes. In the second half, we stayed in the locker room," said Racing manager Laurent Travers.
"It's a big disappointment."
Elsewhere Clermont got their campaign going with a 33-24 win at home against Pau.
Alivereti Raka scored two of Clermont's four tries with Damian Penaud and Arthur Iturria also touching down.
Elsewhere Brive beat Perpignan 17-6.