"I'm very happy. We played really well," Ranieri told reporters. "The players reacted well in the second half with their pride at stake.
"At half time I asked them to just stay calm. We played well in the first 20 minutes of the first half, but we lost our heads a bit when [Jeremy] Toulalan went off injured. But in the second half, we played really well and tightened up in the middle of the park.
"I'm curious to see how my team's play develops; there is history to be made. The atmosphere was electric tonight. Marseille have a very good side and play good football. But we managed to find the right moments to score and get the win."
Lucas Mendes had given Marseille a first-half lead, before Monaco struck twice in the second half.