Lyon rebounded from a disappointing European campaign to beat third-place Toulon 27-12 on Saturday to jump to first place in Top 14, at least for a day.
Toulon slid to fifth after La Rochelle and Racing 92 both won.
Racing were able to start Finn Russell, thrown off the Scotland Six Nations squad on Thursday, as they gained a bonus-point victory in Castres.
Lyon had ended a limp Champions Cup pool stage with a home loss to Northampton.
"I was furious last week, after the loss to Northampton," said Pierre Mignoni the Lyon coach. "It was borderline shameful. We're lucky to have a nice crowd. Elsewhere, we'd have been whistled."
Against Toulon, Lyon put on a show, running in three tries and conceding none to collect a bonus point.
"I've got my team back," said Mignoni "I'm not talking about the victory or the bonus point. I had the feeling that we were lost, that we weren't there. Today we were there."
Anthony Belleau kicked four first-half penalties for visiting Toulon but they could not turn pressure into tries.
Lyon moved two points clear of Bordeaux-Begles, who visit Toulouse on Sunday, but more importantly opened a 12-point gap on La Rochelle as the season entered its second half.
The top six finishers qualify for the playoffs with the top two receiving a first-round bye.
In Lyon, the home team carved Toulon open after seven minutes and Kiwi fullback Toby Arnold, who played a role in all three tries, finished the move by putting winger Xavier Mignot in the corner.
Fly-half Jonathan Wisniewski, who had an impressive afternoon orchestrating Lyon attacks, kicked the first of his three conversions. He also booted two penalties.
"Not everything was perfect, but it was a great afternoon" Wisniewski said. "We were tense in the first half...but we broke free in the second. We took risks."
Belleau kicked Toulon to a two-point lead by the break but Lyon hit back three minutes into the second half.
Arnold dummied and then jinked through the first line of Toulon defence before passing to Josua Tuisova who put winger Rudi Wulf in for a score.
- Careless errors -
Toulon made a series of careless errors. After 57 minutes, they made a mess of collecting a high kick. Arnold swept up the loose ball, again zigged through the defence and then accelerated to score himself and give the home team a 15-point cushion and a potential bonus point.
"We were missing something essential this afternoon: humility," said Toulon coach Patrice Collazo.
Racing were without French squad members Camille Chat, Bernard Le Roux, Boris Palu, Virimi Vakatawa and Teddy Thomas but they unexpectedly had Russell.
The Scot missed a first-half penalty but his tactical kicking played a role as ruthless Racing scored three tries even though hosts Castres dominated the half.
After Castres hooker Marc-Antoine Rallier was sent off for a shoulder charge in the 49th minute, Racing added one more try as they cruised to a 27-0 victory.
In La Rochelle, Arthur Retiere scored three of the home team's four tries as they raced to a 21-point lead over Montpellier, who started the weekend in sixth.
But the home team lost their cool after Montpellier hit back with two tries. Centre Geoffrey Doumayrou was sent off for upending Frans Steyn in a tackle. Despite a fourth Montpellier try, the home team held on to win 35-30, but without a bonus point.
Toulon's Anthony Meric and Raphael Lakafia close in on Xavier Mignot, one of the Lyon try scorers
Finn Russell was in the thick of the action as Racing 92 won in Castres