Marta Kostyuk put together arguably the best performance of her 2025 season at the National Bank Open earlier on Thursday, July 31. She defeated Daria Kasatkina in three tight sets to reach the fourth round of the tournament. Following her victory, she proceeded to shake hands at the net with the World No. 18, who recently changed her allegiance from Russia to Australia. The Ukrainian's actions have since received mixed reception on social media.For those unaware, Kostyuk has actively snubbed Russians and Belarusians at the net since the Russia-Ukraine war broke out more than three years ago. The 23-year-old, along with her countrywomen Elina Svitolina and Dayana Yastremska, has refused to greet them after matches, for which she has received considerable flak.However, Marta Kostyuk seemingly made an exception following her third-round win in Montreal on Thursday, going out of her way to shake hands with 15th-seeded Daria Kasatkina after beating her 3-6, 6-3, 7-6(4) in two hours and 28 minutes. A journalist pointed out the incident on X later on Friday, August 1, claiming that it was out of character for the World No. 28 to shake hands with Kasatkina even if she recently defected from Russia."It's a crazy ol' world they occupy. Now that Kasatkina represents Australia, despite being very much Russian, the handshakes are back on again," they wrote on X.In response to the above tweet, a fan counterargued that since Daria Kasatkina no longer chose to "align" herself with the Russian flag, it made sense for Marta Kostyuk to proceed with the post-match handshake."Not that weird. Kasatkina has chosen not to align herself with russia so why would kostyuk not handshake," the fan wrote.A few others also chimed in with their opinions as Kostyuk became the source of their ire."Marta’s a wierdo for having one-sided beef with the russian and belarusian players," another insisted."But they still shake hands with Americans and Brits... Without whom this war would never have happened," one more asserted."Hypocrisy as it finest," another claimed.One fan, meanwhile, mentioned how Kasatkina had staunchly been against Russian politics in the past, which was likely one of the factors behind Kostyuk's change of heart."Makes perfect sense to me. Kasatkina’s always been against Russia’s invasion of their country, and now she’s even defected," they wrote."It’s really not complicated at all. Many pointed out, the act is bigger than an individual involved in the match. If a player represents a country they are at war with, they’re not going to engage with them. Kasatkina actively took a stand against Russia & doesn’t represent them," another fan wrote.Marta Kostyuk, meanwhile, has overturned a six-match losing streak with her Canadian Open campaign this week and will next face 28th-seeded McCartney Kessler for a quarterfinal berth at the WTA 1000 tournament.Marta Kostyuk had also shaken hands with Daria Kasatkina at this year's Italian OpenMarta Kostyuk reacts after beating Daria Kasatkina at the Italian Open in May 2025 | Image Source: GettyDaria Kasatkina first came out with the news of her applying for permanent residency in Australia around four months ago. A few weeks after the Russian-born World No. 8's decision, Marta Kostyuk ran into her in the second round of the Italian Open.The Ukrainian made quick work of her higher-ranked opponent back then, coming out on top by a scoreline of 6-4, 6-2. The two players greeted each other at the net after their clash.It subsequently became a hot topic in the tennis community on social media for the next few days.