La Rochelle claimed just their second away win of the season on Saturday, running in four tries to defeat Toulon 34-29 and set up a French Top 14 semi-final against Toulouse.
Ronan O'Gara's side will now have the chance to enact revenge upon the team that beat them in last year's Top 14 final -- Toulouse emerged 29-26 victors against La Rochelle in the 2023 showpiece.
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"We put in a very good performance but we're still a long way from a perfection," said La Rochelle captain Gregory Alldritt.
"It's encouraging because it makes us want to get back to work and raise our game."
Toulon, playing in the post-season for the first time since 2018, were indebted to full-back Melvyn Jaminet's kicking accuracy for all of their 15 points in the first half.
However, they were trailing 24-15 by that stage with fly-half Antoine Hastoy, winger Dillyn Leyds and centre Jules Favre all scoring tries as La Rochelle opened a nine-point lead.
After the interval, penalties and errors proved costly for Toulon and they quickly conceded a fourth try when flanker Oscar Jegou crossed.
Hastoy kicked his fourth conversion as La Rochelle stretched their advantage to 31-15.
La Rochelle forwards Will Skelton and Judicael Cancoriet were both yellow-carded in the last 10 minutes.
Toulon were awarded a penalty try before English hooker Jack Singleton cut the gap further with a try with the last move of the game.
"We're going to come back even better," said Toulon director of rugby Pierre Mignoni.
"La Rochelle have a lot of experience. They've won more titles recently than we have. It hasn't been a disastrous season, but it's hard to lose at home like that."
On Sunday, Bordeaux-Begles face Racing 92 in the second play-off with the winners to tackle Stade Francais for a place in the final.
