Top 14 leaders Lyon crumbled in the second half in Paris on Saturday as they suffered their first defeat of the early season, beaten 31-10 at Stade Francais.
Earlier Perpignan, who survived a relegation playoff last season, upset Champions Cup holders Bordeaux-Begles 38–25.
With Pau in action in the late game and Montpellier visiting champions Toulouse on Sunday in a rematch of last year's Top 14 final, Lyon remained top for the time being.
The only other top-six team in action on Saturday afternoon were Bayonne, who salvaged a 20-17 victory at Racing 92 when Ewan Johnson scored with three minutes to go.
In a battle of the two winless teams, Gael Fickou scored his first try for Toulon, who fought back in the second half to beat visiting Vannes 28-10.
In Paris, centre Iosefo Masi put Lyon 10 points up with a 27th-minute try. Home scrum-half Tawera Kerr-Barlow scooted over for Stade Francais before the break.
Stade pressed in the second half and after centre Jeremy Ward put the hosts ahead in the 48th minute, Lyon conceded a string of niggly penalties as the Parisians' forward power told.
Yellow cards for scrum half Baptiste Couilloud and four minutes later flanker Beka Saginadze cost Lyon dearly.
Three substitutes finished Lyon off. Juan Martin Scelzo scored against 13 men, Thibaut Motassi
added a fourth against 14 and Lucas Peyresblanques scored in the last minute.
At half-time we told ourselves that despite Lyon's dominance, it was only 10–5 and we were still in it," said Stade flanker Ryan Chapuis.
"There was a lot of frustration in the first half, we had possession but it was very unproductive.... The second half was much better."
Lyon started last season with three wins before collapsing.
"I don't think the score really reflects the match, but in the end we cracked a bit in the battle of wills," said their hooker Guillaume Marchand.
"I don't think we're in the same rut as last season."
- 'YOU NEED CHARACTER' -
A week after suffering a 50-point thrashing at Montpellier, Perpignan showed clinical efficiency against Bordeaux-Begles, scoring five tries, two while a man down.
"We made loads of mistakes, but what we'll take away from this is the players' spirit," Perpignan prop Enzo Forletta told Canal+.
"The aim in these big matches is to never give up until the very end. When you're up against the European champions, you need character -– otherwise you can't achieve anything."
After giving the hosts the lead with a dazzling ninth minute try, winger Theo Forner earned an 18th
minute yellow card for obstruction.
His team responded with two tries, first from centre Diego Mascarenc and then from hooker Sama Malolo.
The visitors, who again rested star winger Louis Bielle-Biarrey and were also without injured fly-half Matthieu Jalibert, were clumsy and sloppy.
Tety still hit back with tries either side of half time from No.8 Tom Willis and centre Nicolas Depoortere.
Perpigan replied with a solo effort from scrum-half James Hall in the 53rd minute.
Flanker Marko Gazotti cut the gap to six points but Tristan Tedder sealed victory on the final whistle. The full back converted his own try to finish with 16 points.
"We had possession and control throughout the match," said Bordeaux's Maxime Lucu.
"We had opportunities. The opposition scored three tries from three attacks –- that's what decided the match. When we don't score, we get counter-attacked, and in the end that cost us dearly."