Elie Baup's men beat Evian 1-0 on Sunday afternoon thanks to Morgan Amalfitano's first-half goal which ensured L'OM maintain their perfect 100 per cent record with six wins out of six.
"Tonight [Sunday] was a tough match. Our legs were a bit heavy after the trip to Istanbul [to face Fenerbahce in the Europa League] on Thursday evening," Mandanda told the club's official website.
"But we have gained with the head, and the heart. Since the beginning of the season, we demonstrated a certain mindset, a certain solidarity that we can continue.
"But the championship is still long. We are only in the sixth week. Nevertheless, I am a happy captain."
Marseille currently sit five points ahead of Lyon who face Lille later on Sunday. Baup's side face Valenciennes next weekend before the October 7 clash against Paris Saint-Germain.