Marta Kostyuk defeated Zeynep Sonmez 7–5, 6–7, 6–3 in the first round of the US Open on hard court on 28 August 2025, confirming her status as the pre-match favourite with odds of 1.24 to Sonmez's 4.53. The Ukrainian secured the opening set after a tight opening phase, then was drawn into a competitive second set that required a tiebreak, which she ultimately lost. Kostyuk regrouped decisively in the decider, breaking clear in the third set to advance. The result extends Kostyuk's presence in the draw as she pursues a deeper run at the year's final major.