David meets Goliath on Saturday when France's most successful-ever club hosts first-time play-off qualifiers in a barrage.
Christophe Urios' side needed the help of Saturday's opponents to reach the play-offs for the first time in their history, with Toulouse grinding out a win at home to Bordeaux-Bègles despite Census Johnston's first-half red card.
Bordeaux had the chance to nick it, and finish sixth ahead of Oyo, only for Lionel Beauxis to put a last-gasp penalty wide from in front of the posts.
As a result Oyonnax will have the chance to put right a result where they feel they were cheated on the opening day of the season, when they went down by a point in Toulouse with a contentious late turnover for Yannick Nyanga proving crucial.
The tiny club from the east of France have built their success around a simple game plan: a powerful pack of forwards and an unerring kicker in Benjamin Urdapilleta.
They do have some threats out wide, but their plan will be to keep this as tight as possible, and take advantage of Toulouse's struggles up front to keep the scoreboard ticking over.
With Johnston suspended it will be up to Neemia Tialata to hold the fort at tighthead, with very little back-up in case he struggles.
While Toulouse have been up and down this season, their scrum has been the biggest problem, and when it fails they find themselves under huge pressure.
As rank outsiders, Oyonnax should have no pressure on them, but that lack of experience can go both ways. Toulouse certainly have everything to lose, but will the big occasion get to Oyonnax?
Oyonnax have shown they aren't afraid of playing away against the biggest teams, having knocked off both Stade Français and Racing-Métro on their own patches, as well as a second string Clermont at the Marcel Michelin, with a rematch of that game their reward for a win here.
Saturday's game will also pit two of the best sides of the second half of the season against one another, with both having been in the relegation zone after seven rounds of matches.
The key will likely be whether Toulouse can do enough up front to be able to unleash their backs. They were unable to do so when the teams met in Oyonnax in March, but the conditions should be much better this time around.
Still, there is a fragility to this Toulouse team, who have not won a knockout game of any kind since a barrage against Racing in 2013 and if Oyonnax keep it tight, those nerves will start to kick in.
Ones to watch: When the two sides met in March, Guy Novès chose the greater physical presence of Jean-Marc Doussain at scrum-half, but it will be Sébastien Bézy who gets the nod this time around. The 23-year-old is a livewire and it's no coincidence that Toulouse's best performances have come with him running the show. If he can maintain this form, he'll be part of France's plans for next year's Six Nations.
For Oyonnax this will be the perfect opportunity for loosehead Antoine Tichit to enhance his growing reputation. The 25-year-old is not the most technically sound scrummager, but he was able to cause Census Johnston all sorts of problems a couple of months ago, and could do the same to Tialata. If Oyo get the upper hand in the set-piece, they can cause an upset. If Tichit doesn't dominate, the underdogs will be up against it.
Prediction: This should be much closer than it looks on paper, and having rested their usual starters last week, Oyonnax will be fresh. Toulouse were beaten at this stage last season by a team with a similar game plan to Oyonnax and there's every chance it will be the same again. Still, we think Toulouse might have just enough, so we'll go with them to sneak through. Toulouse by 2!
Toulouse: 15 Maxime Medard, 14 Vincent Clerc, 13 Florian Fritz, 12 Luke McAlister, 11 Yoann Huget, 10 Toby Flood, 9 Sebastien Bezy, 8 Louis Picamoles, 7 Yannick Nyanga, 6 Thierry Dusautoir, 5 Patricio Albacete, 4 Yoann Maestri, 3 Neemia Tialata, 2 Corey Flynn, 1 Gurthro Steenkamp.
Replacements: 16 Julien Marchand, 17 Cyril Baille, 18 Joe Tekori, 19 Gillian Galan, 20 Jean-Marc Doussain, 21 Yann David, 22 Timoci Matanavou, 23 Dorian Aldegheri.
Oyonnax: 15 Florian Denos, 14 Silvere Tian, 13 Pierre Aguillon, 12 Hemani Paea, 11 Alaska Taufa, 10 Ben Urdapilleta, 9 Fabien Cibray, 8 Viliami Ma'afu, 7 Olivier Missoup, 6 Maurie Fa'asavalu, 5 Thibault Lassalle, 4 Leon Power, 3 Marc Clerc, 2 Jody Jenneker, 1 Antoine Tichit.
Replacements: 16 Paul Ngauamo 17 Ruaan du Preez 18 Valentin Ursache 19 Pedrie Wannenburg 20 Yohan Domenech 21 Regis Lespinas 22 Roimata Hansell-Pune 23 Soane Tonga'uiha
Date: Saturday, 29 May
Venue: Stade Ernest Wallon, Toulouse
Kick-off: 16:30 local (15:30 GMT)
Referee: Jérôme Garcès
Assistant Referees: Laurent Cardona, Thomas Dejean
TMO: Eric Gauzins