Facing an opponent eager to showcase her not inconsiderable talents on the biggest stage, Halep fought back to complete a 4-6, 6-2, 6-3 victory.
Despite opening up an early lead, Halep was unable to subdue her livewire opponent in the first set. The Japanese teenager reeled off the final three games amid a flurry of winners that had the Suzanne Lenglen crowd roaring its approval.
With the No.6 seed on the ropes, she then had the chance to take a stranglehold of the contest at the start of the second only to fluff her lines when presented with a routine half-volley on break point.
Halep, who finished runner-up in Paris two years ago, made her pay, breaking to love the following game when she expertly steered a forehand into the corner. While this break did not last for long, the Romanian battened down the hatches to force a decider.
Osaka continued to go for her shots, sublime winners of either wing helping eradicate an early break. In the end, though, it was Halep's greater consistency that won the day, an angled cross-court backhand giving her the decisive break in the eighth game before calmly serving out.
For Osaka, it was a case of so near but yet so far. However, talking to the press after the match she was keen to accentuate the positives. "I think I had opportunities, because I did win the first set. I don't think I really enforced my game on her, and I was making too many unforced errors.
"But, I mean, she has more experience than me, so I feel like I'm not the greatest player ever, so I can't be upset that I lost. I'm just going to take this as like a learning lesson, because it's better than how I played in Australian Open third round, anyway."
The win was all the more significant for Stosur considering her miserable record against the Czech going into the match. Stosur had won just three of their 14 meetings, but turned the tables in dramatic fashion this time, breaking in the final game.