Young midfielder Corentin Tolisso's winner saw Lyon inflict Monaco's third defeat of the fledgling Ligue 1 season.
Lyon forward Alexandre Lacazette has signed a new two-year contract, the club have announced.
Zlatan Ibrahimovic scored a hat-trick in Paris Saint-Germain's 5-0 win over Saint-Etienne, while Lyon were beaten again.
Metz scored twice in the last 10 minutes to beat Lyon 2-1 on Sunday.
Lens picked up their first win of the new season with a 1-0 success at Lyon.
Monaco and Lens won 1-0 away to Nantes and Lyon respectively in Ligue 1 on Sunday, as Saint-Etienne and Rennes drew 0-0.
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