Marseille edge Sochaux to set up PSG final
The top-flight strugglers were poor for much of the game, but Florian Thauvin scored the only goal shortly after half-time.
It was the first match back in charge for OM interim coach Franck Passi, after he also stood in earlier this season in the aftermath of Marcelo Bielsa's shock resignation, and he was pleased with how the team reacted to Michel's departure.
"I'm proud of my players. They had a challenge and they rose to the occasion," Passi said.
"The point was to take Marseille to the Stade de France, it was our only door (to save our season) and the players were wide awake tonight.
"This season has been crazy so let's be crazy, we will push PSG in the final."
Passi gave just a second start of the season to injury-plagued midfielder Abou Diaby and partnered Steven Fletcher with Michy Batshuayi in attack, but Marseille were toothless in the opening 45 minutes.
Sochaux have used the confidence found in a Cup run that has seen them beat Bastia, Nantes and Monaco from the top flight, to embark on a five-match unbeaten streak and move away from danger of relegation to the third tier.
In a dire first half the hosts had the only chance of any note, but after Benjamin Mendy could only partially clear, Florian Martin blazed his effort well wide.
Marseille came out after the interval in improved form and took the lead when much-maligned winger Thauvin, on loan from Newcastle United, collected Fletcher's pass, before racing past his marker and finishing coolly at the near post.
Albert Cartier's Sochaux had plenty of possession in the last half an hour but barely threatened an equaliser.
The closest they came was through a Raphael Caceres free-kick which sailed harmlessly over.
PSG edged to victory at Lorient on Tuesday night, as Zlatan Ibrahimovic grabbed the winner 15 minutes from time with his 42nd goal of the season.
Laurent Blanc's men are still targeting a domestic clean sweep of trophies ahead of the French League Cup final against Lille on Saturday.