Fabian Lemoine's goal was all that separated Saint-Etienne and Guingamp over 90 minutes at the Stade Geoffroy-Guichard.
Another win sees Les Verts maintain their 100% start to the Ligue 1 campaign and join Lyon at the top of the table.
Christophe Galtier's men took the front foot early on and were a particular threat from set pieces. However, it was not until the second half until their dominance was finally rewarded.
There was only one thing in Lemoine's mind as he wound up from 25 yards and he executed it to perfection, firing into the top right-hand corner.
The visitors came out of their shell more after conceding, with decent chances falling to Christophe Manganne and Jonathan Pereira before the final whistle.
However, it was Claudio Beavue who came closest to rescuing a point but found Stephane Ruffier in top form as his effort looked destined for the top corner.
