Monaco withstood a barrage of attempts from Gazelec Ajaccio to snatch a 1-0 victory at the Stade Ange Casanova.
David Ducourtioux was penalised for handball after 17 minutes, allowing Fabinho to fire his penalty past Clement Maury.
Gazelec, who have yet to score in Ligue 1 this season, fired in 24 shots over the 90 minutes but were unable to find an equaliser, with Guido Carrillo denied a second-half equaliser after his header was ruled out for offside.
They remain bottom of the table, while Monaco move up to eighth after Bastia were thrashed 4-1 by Marseille at the Stade Velodrome.
Benjamin Mendy’s sensational strike from distance put the home side in front before Romain Alessandrini slammed home a second less than a minute after half-time.
Some good interplay with Javi Manquillo allowed the former Rennes man to double his tally and Michy Batshuayi converted Mendy’s cross for the fourth, before Brandao headed in a consolation against his former club.
Rennes earned the derby bragging rights with a 2-0 victory away to Nantes, meanwhile, who were reduced to nine men.
The home side, who have won just one of their last 10 meetings with their local rivals in Ligue 1, saw Adryan sent off in dubious fashion for a challenge on Edson Mexer on 52 minutes before Paul-Georges Ntep bundled the ball in to put Rennes in front.
Kolbeinn Sigthorsson was given his marching orders for a poor tackle on Mehdi Zeffane before former Nantes youth striker Giovanni Sio secured the points in the dying minutes.
Rennes are now just a point behind champions PSG at the top of the table.