Lille halt St Etienne's winning run
Salomon Kalou scored from the spot in the 37th minute, sending Saint-Etienne goalkeeper Stephane Ruffier the wrong way. Kalou won the penalty when he forced his way into the area between Francois Clerc and Jeremy Clement, and was bundled over by Clement.
It was the first goal Saint-Etienne had conceded in the league this season.
Both sides struggled to create chances. Lille almost doubled its tally in the 66th minute but Ruffier pulled off a brilliant save to parry a fierce, swerving shot from Ronny Rodelin.
The result means Marseille is the only team to still have a perfect record after three matches..