Goals from Ludovic Blas and Randal Kolo Muani gave Les Canaris a vital win on their opponents' turf on Thursday night, but a stunning drive from Deiver Machado has kept Toulouse's promotion hopes alive.
Antoine Kombouare's stint in the Toulouse dugout was one of the most forgettable affairs of the 57-year-old's managerial career so far, but he managed to get one over his former club at a crucial time with a 2-1 success at the Stadium de Toulouse in the first leg of the playoff.
The ever-improving Blas put Les Canaris ahead with his 11th strike of the season before Toulouse left-back Machado restored parity with a powerful effort from long range, but Kolo Muani was on hand to tap home in the 22nd minute after some strong play from Kalifa Coulibaly inside the area.
Les Canaris had plenty of opportunities to kill the tie off in the second period but ultimately had to make do with a one-goal success before Sunday's second leg, and Kombouare has affirmed that his crop must remain "serious and humble" as they seek to avoid relegation to Ligue 2 for the first time since 2009.
Nantes were one of the in-form sides before the regular Ligue 1 season came to a close and welcome Toulouse to Brittany having won five of their last six, although four of those wins have come on the road and they can only boast a solitary success from their last 17 at home.
Kombouare's side blew their opportunity to confirm survival in Ligue 1 on the final day of the season against Montpellier HSC, but 90 minutes now separates them from another season in the big time, and that would be no less than Les Canaris deserve given their revival in the business end of the campaign.
Toulouse are in no position to roll over and let Nantes waltz through to another season of top-flight football, though, especially seeing as they let automatic promotion slip through their grasp and are now fighting an uphill battle to return to the top table.
Patrice Garande's men had strung together a 14-game unbeaten run on home soil before being bettered by their top-tier opponents, and should they fail to overturn the deficit in Sunday's second leg, they will no doubt rue the missed opportunities to secure a top-two finish in the Ligue 2 campaign.
Nantes are not exactly renowned for any sort of superiority on their own turf, but Toulouse's downfall in the second half of the season largely came on the road, as Garande's side have only won one of their last nine away from home - losing five and drawing the other three in that run.
A team that was consistently challenging for top-seven finishes in Ligue 1 10 years ago spending a second successive season in Ligue 2 would represent a major downfall in fortunes, but Garande - as expected - has refused to throw in the towel just yet, as Toulouse have another 90 minutes to secure an immediate return to top-division football.
Toulouse's most recent victory away to Nantes came in the 2014-15 season, though, and Les Canaris have come up trumps in the last four meetings at the Stade de la Beaujoire in all competitions, netting at least two goals each time.
Nantes are once again well-stocked for the second leg and have no new injury concerns from Thursday's game, although Kombouare admitted that there were several tired legs on the Toulouse turf given the hectic schedule.
The hosting manager will likely demand his big-hitters to push through for another 90 minutes before the season draws to a close, but Sebastien Corchia is ready to provide freshness at right-back if needed.
Kolo Muani joined Blas in the double-figure scoring charts with his decisive finish in the first leg, and the 22-year-old ought to partner Coulibaly up top for the final time this term.
Toulouse coach Garande can call upon Steve Mvoue after he completed a two-game suspension, but the 19-year-old certainly will not be considered for a start in a game of this magnitude.
Nantes possible starting lineup:
Lafont; Corchia, Castelletto, Pallois, Traore; Blas, Louza, Chirivella, Simon; Kolo Muani, Coulibaly
Toulouse possible starting lineup:
Dupe; Amian, Dewaest, Gabrielsen; Moreira, Kone, Spierings, Van den Boomen, Machado; Healey, Bayo
We say: Nantes 1-1 Toulouse
Should Healey be given the chance to influence the encounter from the first whistle, Toulouse ought to feel confident about their chances of breaching a Nantes defence which is by no means impenetrable.
However, Les Canaris have quality in abundance at the other end of the pitch - although they may be tempted to shut up shop and hold on to what they have - and when taking into account the hosts' home woes and the visitors' away day struggles, we expect the second leg to end all square as Nantes survive by the skin of their teeth.