The Red and Whites made it five wins from their last six matches at Stade Gerland and maintained the eight-point gap in second place after champions PSG claimed a 2-0 win over St Etienne later on Sunday.
Ranieri's men raced into an early two-goal lead thanks to goals from Valerie Germain and James Rodriguez before Jimmy Briand offered the hosts hope with a strike before half-time.
However, Dimitar Berbatov was on hand shortly after the restart to restore Monaco's two-goal advantage before Briand added what turned out be a consolation with 12 minutes left.
Ranieri told his club's official website: "It was a very difficult game against a very good Lyon team.
"I'm happy with the way my players (performed). It's not easy to score three goals against Lyon and even less to leave Lyon with three points."
For former Tottenham and Manchester United striker Berbatov, his goal after 52 minutes was his second for the Ligue 1 high flyers since his January arrival from Fulham.
The 33-year-old, who also scored in last weekend's 2-1 victory over Sochaux, was pleased to get on the scoresheet again, and said: "It gets better every game, goals are scored, (we take) the points back to the house and everyone is happy."
Monaco are next in action when they take on third-placed Lille in the league next Sunday at Stade Louis II.