Les Bleues were rarely troubled by a limited South Korea side and took only nine minutes to open the scoring, with Eugenie Le Sommer firing the ball into the roof of the net from close range.
Wendie Renard doubled the tally with a downward header in the 35th minute, and the towering defender added another with her head on the stroke of halftime.
France's intensity dropped after the break but the stadium was sent into raptures again five minutes from fulltime when captain Amandine Henry curled a superb shot into the far corner of the net.
"We worked a lot, they suffered a lot during the preparation period. I've had time to prepare things, it's a luxury. We won tonight but it's just the first step," Diacre told a news conference at the Parc des Princes.
"We need six more (steps) to reach our goal, we must keep our feet on the ground and keep working."
France played the perfect game, reaching the interval with a three-goal lead that all but extinguished South Korea' hopes of victory.
"We started well, it was the way to go we made it easy for ourselves. It was important to score a second goal before the break, we did even better," said Diacre.
Woman of the match Wendie Renard told reporters: "We knew there would a be a lot of emotions tonight, we dealt with it perfectly.
"This victory will do us good. I had never scored at a World Cup but it's important collectively and those goals helped us reach halftime with a three-goal lead."
France next face Norway, who play Nigeria in the other Group A game on Saturday.
(Reporting by Julien Pretot; Editing by Toby Davis)
