Marseille will face holders Paris Saint-Germain in the Coupe de France final following a 1-0 win at Ligue 2 side Sochaux in what was Franck Passi's first game in charge after the suspension of head coach Michel.
Passi stepped up from his role as assistant coach on Tuesday and was indebted to Florian Thauvin for settling this semi-final.
After a poor first half, Thauvin gave Marseille, who are the Coupe de France's most successful club with 10 titles, the lead shortly after the interval, the winger firing in a low finish after being found by Steven Fletcher in the box.
Fletcher went close to scoring a second goal for the visitors, but he was denied by Olivier Werner, while the hosts struggled to create a clear opening.
The victory was Marseille's second in 13 matches in all competitions and set up a showdown with PSG in the final at the Stade de France on May 21.
Interim coach Passi made five changes from the Marseille team beaten 2-1 by Monaco last time out, while Florian Tardieu and Moussa Sao came into the Sochaux side.
Tardieu had the first shot at goal in the third minute, but his curling strike was comfortably caught by Steve Mandanda, before Florian Martin lashed a drive off-target.
Werner saved an awkward bouncing shot by Georges-Kevin Nkoudou after 25 minutes, before Mandanda spilled Karl Toko Ekambi's effort, but recovered to claim the loose ball.
Marseille took the lead three minutes after half-time, Thauvin netting a fine goal.
Fletcher found the winger in space on the right side of the box and Thauvin beat Jeando Fuchs easily and drove a superb strike inside Werner's near post.
Scotland international Fletcher almost added a second after 58 minutes, but his 20-yard shot was beaten away by Werner.
Sochaux made a double change, introducing Florin Berenguer and Yannis Mbombo, but Marseille continued to push, Thauvin sending a 20-yard drive narrowly wide.
Michy Batshuayi had a glorious chance to make sure of Marseille's win after 78 minutes, but the striker somehow put Benjamin Mendy's cross wide from eight yards out.
However, that awful miss did not matter as Marseille held on comfortably to confirm they will face PSG in May's showpiece final.