Clermont's Patricio Fernandez Fiante (L) vies with Lyon's Felix Lambey (R) during their French Top 14 rugby union match at the Matmut Stadium de Gerland in Lyon, central-eastern France
Clermont stayed on course for a French and European double when they edged Lyon 23-20 to move into second place in the Top 14 as La Rochelle confirmed their semi-final spot without even playing.
Clermont, who were missing a host of first-choice stars such as Aurelien Rougerie, David Strettle, Camille Lopez and Morgan Parra ahead of the May 13 European Cup final against Saracens, have 74 points.
However, they can be displaced on Sunday if Montpellier defeat league leaders La Rochelle.
Clermont's failure to claim a bonus point means that La Rochelle, already on 80 points, are guaranteed a semi-final place.
Lyon were in the ascendancy early on and went ahead when back-rower Deon Fourie scored one of his team's two converted tries in the 11th minute after Clermont winger Remy Grosso had been yellow-carded for a deliberate knock-on.
But 22-year-old Fijian winger Alivereti Raka grabbed Clermont's only try on the quarter-hour mark with three penalties from Ludovic Radosavljevic and one successful kick from Argentie fly-half Patricio Fernandez helping them to a 17-10 lead at the break.
Radosavljevic knocked over two more penalties in the second period while replacement prop Stephane Clermont scored a late converted try for Lyon whose play-off hopes were almost certainly ended.
"It was a good performance even if we were living on our nerves towards the end," said Clermont coach Franck Azema.
"We committed some youthful errors but showed a lot of character."
Three-time European champions Toulon also wrapped up a play-off spot with a 26-13 win at Bordeaux.
Welsh full-back Leigh Halfpenny kicked 16 points including conversions of his team's two tries, an 11th-minute opener from hooker Guilhem Guirado and Australian No8 Liam Gill six minutes from time.
Jean-Marcellin Buttin crossed in the last minute for Bordeaux whose slim play-off hopes were extinguished with defeat.
- Toulouse humbled -
Castres' Argentinian fly-half Benjamin Urdapilleta orchestrated a six-try, 52-7 thrashing of Toulouse that deprived the 19-time French championship winners a place in the play-offs for the first time since 1976.
Urdapilleta scored his team's fourth try and also contributed 22 points with his unerring boot in helping consign Toulouse to a ninth defeat in 10 matches that leaves them rooted in 12th position in the table, above only relegated clubs Grenoble and Bayonne.
The result saw Castres move to fifth place on 63 points and guaranteed a play-off sport.
Alex Tulou, for Castres, and ex-All Black Luke McAlister, for Toulouse, each crossed for first-half tries.
But with Urdapilleta chipping away at the scoreboard, the floodgates soon opened in the second half, Julien Caminati twice, Brice Mach and Julien Dumora all crossing the whitewash in a totally dominant, bonus-point performance by the home side.
Toulouse coach Ugo Mola, who took over from Guy Noves when the latter moved to the France job, said the result summed up a "complicated" season.
"Today we saw the difference between a team that still has something to play for and one which very definitely let go," the former France full-back said.
"Pride has taken a hit. We're closer to shame than anything else."
Despite already being relegated, Bayonne and Grenoble put on an entertaining show with 10 tries between them in the home team's 43-35 win.