Elsa Jacquemot defeated Marta Kostyuk 6–7 7–6 7–6 in the first round of the Australian Open on hard court on 18 January 2026, delivering a major upset against the heavy favourite. Kostyuk entered with odds of 1.07, making her the overwhelming pre-match favourite, whilst Jacquemot was a 7.83 outsider. The match proved remarkably tight across all three sets, each decided by a single break or tiebreak, with neither player able to establish decisive separation. Jacquemot's ability to stay composed in the closing moments of consecutive tiebreaks proved the difference in a contest that defied the betting odds. The result marks a significant scalp for Jacquemot early in the season and suggests considerable resilience under pressure in a Grand Slam environment.