Brock James and La Rochelle survived a late scare to defeat Montpellier 40-37 as they secured top spot in the Top 14 and can now prepare for a home semifinal.
Willie du Plessis touched down inside four minutes for Montpellier who last week crushed Racing 92, 54-3, but a Jeremie Maurouard try and three penalties from James helped the home side to a 16-13 halftime lead.
The game looked over after tries from Kevin Gourdon, Pierre Aguillon and a brace from Victor Vito put La Rochelle into what looked like a comfortable 40-16 lead going into the final 10 minutes.
But they turned off after referee Romain Poite awarded a penalty try with six minutes remaining and they almost came undone.
Nemani Nadolo and Duhan van der Merwe added tries before a last minute turnover for Montpellier gave them one last chance, but having chased a kick through the TMO deemed Nadolo failed to ground the ball under pressure and La Rochelle escaped with the victory.
Stade Francais got the bragging rights in Sunday's Parisien derby with a 27-23 victory over Racing 92.
Dan Carter and Jules Plisson twice exchanged penalties in the opening half and when Juan Imhoff's try was chalked off by the referee, it seemed as though the game could fizzle out.
But in the final 10 minutes of the half, the game burst into life. First Sergio Parisse intercepted a pass from Carter to run in under the posts. Then Pascal Papé and Wenceslas Lauret saw red three minutes from the break after Papé struck Henry Chavancy and Lauret responded by striking Papé.
At the end of the half Carter made up for his earlier mistake as he burst through the Stade defence, before a delightful offload saw Casey Laulala run in to score to level the game.
Seventeen seconds after the restart Stade were back in front as the ball went through the hands from Geoffrey Doumayrou and Jules Plisson and as Brice Dulin slipped to take out Joe Rokocoko, Djibril Camara brushed past Chavancy to score in the corner.
Five minutes later, Jonathan Danty received the ball outside the Racing 22, and with Dulin out of position, he chipped ahead and outsprinted Rokocoko to touch down. Ben Tameifuna crashed over for a try and Carter added a penalty for Racing but it wasn't enough as Stade held on for the win.
Leigh Halfpenny kicked 16 points as Toulon secured a playoff place after a 26-13 win at Bordeaux Begles.
The win was never in doubt as Guilhem Guirado's converted try and three Halfpenny penalties helped them to a 16-3 lead by the half hour.
Bordeaux's Vadim Cobilas and Toulon's Florian Fresia both were sent to the sin-bin following difficulties at the scrum and Toulon ended the half with 13 as Juan Smith joined them on the sidelines.
Baptiste Serin and Halfpenny kicked penalties after the restart, and a Liam Gill try sealed the victory and a quarterfinal spot for Toulon before a late Jean-Marcellin Buttin consolation try for Bordeaux.
Clermont Auvergne didn't have it all their own way as they looked to cement a home semifinal as they defeated Lyon 23-20.
Despite suffering an early blow with former Lyon wing Remy Grosso sin-binned and falling behind to a Deon Fourie try inside 11 minutes, Clermont struck back in style.
Patricio Fernandez received the ball from Radosavljevic off a scrum on the Lyon 22, and a interchange between him and Damian Penaud saw Fernandez release Alivereti Raka on the 22. The Fijian burnt Hosea Gear for pace, sold Delon Armitage a dummy and crashed through centre Hemani Paea to score.
Fernandez converted, and added a penalty before Radosavljevic knocked over two more penalties. Lyon trailed 17-10 at the end of the half despite having both Napolioni Nalaga and Albertus Buckle yellow carded, as Mike Harris and Radosavljevic traded penalties.
Radosavljevic (two) and Harris (one) kicked penalties after the restart but Clermont held on for the win despite conceding a late try to Stephane Clement.
Castres secured a playoff spot after an emphatic 52-7 home win over Toulouse.
Despite having a man advantage when Yoann Huget was sin-binned for a deliberate knock on, Castres led 13-7 at the break with Alex Tulou and Luke McAlister exchanging tries and two penalties from Benjamin Urdapilleta.
But Toulouse failed to show up in the second half and were cast aside with ease as a brace from Julien Caminati and further tries from Brice Mach, Urdapilleta and Julien Dumora saw Castres clinch a playoff spot.
Pau kept their hopes of a playoff spot alive after a 32-27 win over Brive who had playoff aspirations of their own before kickoff.
Brive's Benjamin Lapeyre crashed over 12 minutes in but within five minutes Damien Lavergne was sent to the sin-bin for infringing at the scrum. Pau kicked to the corner and following the lineout Watisoni Votu went over to score. With Lavergne still off the field, Brive hit back through Thomas Laranjeira and a Gaetan Germain penalty which helped them to a 17-7 lead.
Penalties from Tom Taylor and Thibault Daubagna before the break and a second Votu try after the restart revived Pau. Then Lapeyre saw a gap in the home defence to score his second to push Brive back in front, but it wasn't to last.
And it was the Pau forwad pack that turned things around with Quentin Lespiaucq touching down and then having put the Brive defence under pressure, Teddy Iribaren was sin-binned as he tried to stop their march. The referee awarded a penalty try to Pau, which Taylor converted to seal the win.
Bayonne won the battle of the bottom two as they ran in six tries in a 43-35 victory over Grenoble in the south of France.
Bayonne started the brighter with Gabiriele Lovobalavu's kick through bouncing favourably for Martin Laveau for the opening try. But a yellow card for Lovobalavu, for a tackle off the ball, saw Grenoble up the intensity.
Gilles Bosch kicked two penalties and both Fabien Alexandre and Armand Batlle touched down to give them a 21-7 lead. But their lead disintegrated as quickly as it had been built up. Laveau, Lovobalavu (twice) and Kade Poki all touched down to give Bayonne a 36-21 halftime lead.
That is how it stayed until the last quarter when Toma Taufa sealed the victory, and two late Grenoble tries put respectability on the scoreboard.