Gerson scored the opener before Sanchez added the second as Marseille ensured they will end the weekend at least in a share of the lead at the top of the table.
They have won five and drawn one of their opening six matches under new coach Igor Tudor this season, and sit provisionally three points clear at the top from reigning champions Paris Saint-Germain, Lyon and Lens.
However, PSG have a far superior goal difference so will reclaim top spot if they win at Nantes later on Saturday.
Lens go to Reims on Sunday, while Lyon crushed struggling Angers 5-0 on Saturday with Cameroon forward Karl Toko-Ekambi scoring twice.
Marseille head to London to face Tottenham in their opening Champions League game on Wednesday.
The 1993 European champions are in Group D along with Sporting Lisbon and last season’s Europa League winners Eintracht Frankfurt.
Tudor made seven changes to his Marseille line-up following the 1-0 midweek home win over Clermont, in which Sanchez missed a penalty.
The Chilean former Barcelona and Arsenal star was one of those to drop out, while Brazilian international Gerson came in and opened the scoring in the seventh minute in Burgundy.
Cengiz Under hit the post, but Gerson followed up to convert the rebound and make it 1-0.
Arsenal loanee Nuno Tavares came off the bench in the second half and hit the post for Marseille, before Sanchez finished off a cutback from fellow substitute Matteo Guendouzi to make it 2-0 six minutes from time.
Lyon remain unbeaten this season after a Saturday evening stroll against a winless Angers, with Toko-Ekambi opening the scoring before Alexandre Lacazette headed in the second.
Toko-Ekambi scored again just before the hour mark and Castello Lukeba and Moussa Dembele then added further goals.
