Marta Kostyuk has had a career-changing year in 2026. The 24-year-old Ukrainian was excellent in juniors but hadn't completely found herself on the WTA Tour until this year. If someone beats her in the last several months, they tend to go on and win the tournament in which the match took place. That's how good Kostyuk has been.
2017 US Open winner Sloane Stephens learned that on Wednesday in the second round. Kostyuk wasn't just playing at her usual 2026 form early in the match; she was playing at a level that few players can currently match. She laced backhands cross-court for winners, hit kick-serves on second serves that bounced away from Stephens and to her backhand; it was astonishing tennis.
The 6-1 first-set victory for the 11 seed was no joke. She dominated Stephens, who could do nothing else but watch balls pass her. She wasn't even playing poorly; she was simply being soundly beaten by a player in top flight. If she had any hope of a comeback, it would be that Kostyuk would suffer a stunning dip in form.
Marta Kostyuk defeats Sloane Stephens in the second round of the US Open
In the opening set, Kostyuk hit 13 winners and just nine unforced errors while winning 87 percent of her first serves. Stephens could only win 47 percent of those same serves and hit three winners but seven unforced errors.
Even those statistics were a bit of a lie. It was Kostyuk who was putting the American in a position to have to force overhits to try to steal points. Still, one wondered if one set would not make the match, and in set two, Stephens did play better.
While Kostyuk got a break of her opponent early in the set, the games were becoming closer, and it was Stephens who was trending in the correct direction. With the Ukrainian serving at 4-3, Stephens got her own break, and the set was back on serve at 4-all.
At 5-all, though, Kostyuk proved why she is beginning to rise to the top 10 on the WTA Tour, a place she is likely to stay for some time. She began to be even more precise with her groundstrokes, hitting at angles that even Novak Djokovic would be jealous of, and she got the break of Stephens.
The depth on her shots was extreme, and exactly what a coach would teach a young player. Her athleticism was paying off, too, catching up to well-struck shots by Stephens.
Trying to serve out the match, Stephens kept battling, but Kostyuk was too much. The Ukrainian faced a couple of deuces, but came through to take set two 6-4.
Marta Kostyuk will next face either Kimberly Birrell or Ekaterina Alexandrova in the third round of the US Open. She would be favored over both players.
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