Second half goals from Paraguayan Junior Alonso, Nicolas de Preville and Dutch-Moroccan Anwar El Ghazi earned Bielsa a winning return to France two years after walking out of Marseille following the opening game of the 2015/16 season.
“We played with a lot of dynamism, our tempo was very, very high, we made very few mistakes and our goalkeeper was pivotal,” said Argentine Bielsa, 62.
“We’ve been working together for two months and we were desperate to play the first official match.
“It’s far too early to make conclusions about our game, whether that’s the positives or the negatives.”
Ranieri was appointed Nantes coach in June, four months after his sacking by Leicester City, the club he guided to a fairytale Premier League title in 2015/2016.
This was the Italian’s first return to Ligue 1 since leaving Monaco despite leading them to a second placed finish behind Paris Saint-Germain in 2014.
“I wasn’t surprised by Lille’s performance, they’re a very good team with some very good young players,” said the 65-year-old.
“I think they will have an important say in the title race. They were more motivated than us and that’s no good.
“I want my players to be more motivated. We can lose but we cannot lack motivation or aggression.”
Lille, champions of France in 2011, dominated throughout but proved ineffective in front of goal during the first period.
But that all changed after the break and from the moment Alonso opened the scoring three minutes into the second period with a crisp shot from outside the area, Lille never looked back.
De Preville doubled the advantage midway through the half from the penalty spot after Nicolas Pallois felled Kevin Malcuit in the box.
El-Ghazi put the game to bed just three minutes later.
The victory moved Lille up to second behind Lyon, 4-0 winners over newly-promoted Strasbourg on Saturday, in the early table.