Monaco remain top of France's top flight after Radamel Falcao's early penalty clinched a 1-0 home win against Lorient on Sunday.
The Colombia striker, a £51m summer signing from Atletico Madrid, converted his fourth Ligue 1 goal after he was fouled in the sixth minute.
Claudio Ranieri's newly promoted side have earned 13 points from five games.
They are a point ahead of second-placed St Etienne and two clear of defending champions Paris St-Germain in third.
The principality team, who embarked on a lavish summer spending spree totalling over £100m, hit the post shortly before half-time through Brazilian teenager Fabinho.
Lorient posed little threat and the defeat leaves them 13th on six points.