Now ranked 134th in the world, Osaka has never advanced past the last 32 at the French Open, while her four Grand Slam triumphs have come on hard courts.
Osaka reeled off five games in a row to wrap up the first set in just 27 minutes on a gusty Court Philippe-Chatrier.
But Bronzetti grew into the match and, after struggling to challenge Osaka’s serve throughout the second set, converted a crucial break point at 5-4 to force a decider.
Remarkably, the world number 67 clawed her way back from a double break down in the third before Osaka broke once more to regain her lead and serve out the two hour back-and-forth contest.
The victory marks progress for the 26-year-old, who says she is “embracing clay a lot more”, external after previously struggling on the surface.