The German international scored the only goal from the penalty spot in France, making it two wins out of two for the Bavarian giants.
Muller said that Les Dogues showed plenty of spirit, stating that he is surprised how poorly they have started the season.
"We were under real pressure today," said Muller. "The situation wouldn't have been pleasant had we lost or drawn.
"Lille put up a great fight, it's surprising they have not collected any points so far this Champions League campaign.
"It's certainly no easy feat to beat them on their own turf."
Valencia beat BATE Borisov 3-0 in tonight's other game in Group F.