Quarter-finalist in Major for the first time last year in Melbourne, the Frenchwoman who will turn 33 on Sunday had not lost there in the first round since 2012. She will therefore miss a long-awaited meeting with the N.1 tricolor Caroline Garcia scheduled for the second round.
In a strong heat, Cornet started the game by taking the serve of his opponent and confirmed to lead 2-0.
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Australian Open: ladies schedule and results
Australian Open: men's schedule and results
But Fernandez, the 2021 US Open finalist, broke to come back at 3-3 and, after having a first set point on Cornet's serve at 5-4, she scored the decisive break at 6-5.
In the second set, the 20-year-old Canadian broke to lead 4-2 and won the next two games to prevail.
She, who had never won a single match at the Australian Open in three previous appearances, will try Thursday to reach the third round against another Frenchwoman, Caroline Garcia (4th), or her compatriot Katherine Sebov (190th and from qualifications).
