Match ends, Monaco 1, Marseille 0.
Ligue 1's top two teams, Marseille and Paris St-Germain, both lost 1-0 to open up the title race.
Lyon now trail Marseille by only one point and PSG by two after their 3-0 win over Caen on Friday.
Champions PSG lost their first league game of the season as Jeremy Pied scored Guingamp's only goal.
Marseille were beaten by Monaco, last season's runners-up, Bernardo Silva scoring from 16 yards out after a dummy from Yannick Ferreira Carrasco.
Monaco, who cut costs during the summer, moved up to sixth in the table with victory at Stade Louis II.
Marseille handed a debut to 16-year-old Bilal Boutobba late on.
- 24RaggiBooked at 85mins
- 8João MoutinhoBooked at 44mins
- 7DirarSubstituted forOcamposat 78'minutesBooked at 90mins
- 15Bernardo SilvaSubstituted forDialloat 90+1'minutes
- 23MartialSubstituted forGermainat 82'minutes
- 20López Menéndez
- 26Dja Djédjé
- 23MendyBooked at 74mins
- 8LeminaBooked at 45minsSubstituted forBoutobbaat 84'minutes
- 10A AyewSubstituted forBatshuayiat 72'minutes
- Tony Chapron
- Shots on Target
Second Half ends, Monaco 1, Marseille 0.
Corner, Marseille. Conceded by Valère Germain.
Delay over. They are ready to continue.
Delay in match Bilal Boutobba (Marseille) because of an injury.
Lucas Ocampos (Monaco) is shown the yellow card for a bad foul.
Bilal Boutobba (Marseille) wins a free kick on the right wing.
Dangerous play by Lucas Ocampos (Monaco).
Giannelli Imbula (Marseille) wins a free kick in the defensive half.
Foul by Yannick Ferreira-Carrasco (Monaco).
Substitution, Monaco. Abdou Diallo replaces Bernardo Silva.
Foul by Michy Batshuayi (Marseille).
Bernardo Silva (Monaco) wins a free kick in the attacking half.
Corner, Marseille. Conceded by Jérémy Toulalan.
Foul by André-Pierre Gignac (Marseille).
Fabinho (Monaco) wins a free kick in the defensive half.
Attempt saved. Lucas Ocampos (Monaco) left footed shot from the centre of the box is saved in the bottom right corner. Assisted by Bernardo Silva.
Andrea Raggi (Monaco) is shown the yellow card for a bad foul.
Bilal Boutobba (Marseille) wins a free kick in the attacking half.
Foul by Andrea Raggi (Monaco).