Roussin-Bouchard’s overnight four-shot lead turned into a one-stroke deficit with two holes to play before the tournament turned on the penultimate hole.
Having taken the lead with a birdie on the 16th, Argentina’s Magdalena Simmermacher bogeyed the 17th as Roussin-Bouchard made birdie to take a slender lead down the last.
The 21-year-old held her nerve to par the 18th and finish 11 under par, a shot ahead of Simmermacher and Sweden’s Linn Grant, who birdied three of the last four holes to complete a superb 62.
“It was a little bit stressful to be honest, because I played great golf but the putts weren’t going in, and when you see other people making birdies ahead of you it was quite stressful,” Roussin-Bouchard said after her 68.
“But I always say it’s all about the finish and I made a birdie on the 17th, so it definitely was all about the finish.”
Roussin-Bouchard – a former World No.1 ranked amateur – had only become a professional a fortnight ago.
Australia’s Whitney Hillier was one of four players to not drop a shot in the final round, shooting 65 to share eighth spot – her first top 10 finish of the season.
Sydneysider Steph Kyriacou finished in a tie for 10th spot at four under.
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