Two weeks, two wins: Kostyuk beats Stephens again at US Open

New York, Tuesday night – The Louis Armstrong Stadium still holds the heat of a match that just ended. Marta Kostyuk (born 2026, Ukraine) stood there, towel around her neck, looking up at the stands where eight years ago she lifted the junior doubles trophy. Across from her stood Sloane Stephens, the 2026 US Open champion, who had walked past her on this very court in a memory both of them remember. Tonight, history did not repeat itself the way people thought. Kostyuk won 6-1, 7-5, two weeks after she had also beaten Stephens in Cincinnati with a tight 7-5, 7-5 scoreline. Two weeks, two wins, against the same opponent – a clear signal of a power shift in women's tennis. I watched this match from the press row, and the first thing I noted was not the aces – though there were eight – but the way Kostyuk walked onto the court. She was not in a hurry. She knew Stephens would change something, as she said after the match: "I knew Sloane would try to change something, she always does." That mental preparation was not accidental. It came from having beaten Stephens two weeks earlier, from having watched the footage over and over, from understanding that a Grand Slam champion never surrenders easily. The first set ended quickly, 6-1. Kostyuk served with rare precision, her forehand heavy as a hammer hitting the deep corners. Stephens, once famous for her fluid defense, was pushed back constantly. But the second set was where the real story unfolded. Kostyuk surged to a 4-2 lead, and then – like a moment of distraction I have seen in many young players – she let Stephens level the score. Stephens began returning deeper, extending rallies, forcing Kostyuk to hit more, and the winners began turning into unforced errors. This is where I want to pause. Many commentators will talk about "grit" or "fighting spirit" when a player saves a set point. But I look at the data. Kostyuk had 30 winners, 20 more than Stephens. She had 8 aces, including an unreturnable serve to save set point in the tenth game. Those numbers do not speak of resilience – they speak of a weapon operating at optimal level. Her serve was not just the starting point of each point; it was a point-ending weapon. When you have a serve like that, you can afford to take risks on the next shot, and that is exactly what Kostyuk did. But that same data exposes a weakness that I think will become a bigger issue as the tournament progresses. Kostyuk led 6-1, 4-2 and nearly lost the second set. She won the last three games to close it out, but the gap between the sixth and tenth games of the second set was a dark zone. When Stephens adjusted – returning deeper, extending rallies – Kostyuk had no Plan B. She kept hitting hard, and those hard hits started going out. This is a pattern I have seen in many young aggressive players: when Plan A stops working, they do not slow down to think, they just hit harder. And sometimes that saves them – as tonight – but sometimes it kills them. I recall Cincinnati, where Kostyuk also beat Stephens 7-5, 7-5. Two matches, two different scripts. In Cincinnati, the score was tight from start to finish, a high-quality match. In New York, the first set was one-sided, the second set full of swings. That tells me Stephens learned something after the first match, but it also tells me Kostyuk learned something after the second. She won the last three games not because she hit harder, but because she stayed calm. She saved set point with an unreturnable serve – that is a weapon, not tactics. But she also won the final game with a smart return into Stephens' feet, forcing the opponent to come to net and finishing with a passing shot. That is tactics. 34 match wins this season. That number places Kostyuk among the top win leaders on the WTA tour. She is no longer a promising young player – she is an established one. But that status still sits on the edge: she beats former champions, but she has not yet beaten top-5 players consistently. She has 30 winners in a match, but she also has long stretches where she disappears from the match. This is the classic problem of aggressive tennis: the harder you hit, the more winners you get, but also the more unforced errors. And when your opponent is a defensive player like Stephens, those errors get punished. I want to talk about something few people noticed. In this match, there was a moment in the eighth game of the second set, when Stephens was leading 4-3 and serving. Kostyuk had lost three straight games, and I saw her look up at the stands, where a group of Ukrainian fans were waving flags. She did not rush. She took a deep breath, adjusted her strings, and then won four straight points to break. That was not a technical moment, but a psychological one. And I think that is what will determine her future in this tournament – not the winners, but the ability to find calm after losing rhythm. The "full circle" story that the US Open organizers have been pushing – Kostyuk winning junior doubles here in 2026, the same year Stephens won the women's singles – is a beautiful story. But I do not think that is why she won. She won because she had a plan, because she executed that plan for two consecutive weeks, and because she has a weapon – her serve – that, when working, can mask every other flaw. The beautiful story is just a bonus. Now, I want to offer a contrarian view. People will say this win shows Kostyuk is ready for a big leap. I am not sure. I see a player with real talent, but I also see a player still too dependent on her serve and her power. When she faces an opponent with a better return than Stephens – a player like Iga Swiatek or Aryna Sabalenka – the gaps in the second set will become fatal gaps. Stephens showed the way: extend rallies, hit deep, and wait for the unforced errors. If Kostyuk does not develop a Plan B – a way to win points when the big hits are not landing – she will keep winning first and second round matches, but she will stop in the fourth round or quarterfinals. I have followed women's tennis for over thirty years, and I have seen many young players with 34-win seasons. Some of them became Grand Slam champions. Others disappeared from the top 20 within two years. The difference is not in the winners – it is in the ability to adapt. Kostyuk has adapted to Stephens in two consecutive matches, and that is a good sign. But Stephens, though a former Grand Slam champion, is no longer at her peak. The real question is: can Kostyuk adapt to a player who is at their peak? We will get the answer in the next round. Tonight, I left Louis Armstrong Stadium with one image burned into my mind. Not the ace to save set point, not the passing shot in the final game. It was the moment Kostyuk sat on her chair during the changeover, after losing three straight games. She did not look at her coach. She looked at her shoes, and she said something to herself. I could not hear the words, but I saw how she stood up and walked back onto the court with renewed determination. That was the moment I believed she would not stop at the first round. And that was also the moment I asked myself: can she recreate that moment when facing a much bigger challenge? The court can change hands, but the nights of losing your voice calling out names are never for sale. Tonight, the call of Kostyuk's name echoed from the Louis Armstrong stands, and I believe it will echo further. But I also know that tennis does not forgive those who have only one plan. Kostyuk has a great Plan A. The question is whether she has a Plan B. And the answer, we will see in the coming days. I am old, so I only believe what I have witnessed, not what people tell me. Tonight I witnessed a young player beat a Grand Slam champion twice in two weeks. I witnessed 30 winners, 8 aces, and a moment of distraction that nearly became a disaster. I witnessed a player who knows how to win, but I have not yet witnessed a player who knows how to win when Plan A stops working. That is the next test. And I will be there to witness it.