The world No.35 vanquished a second Russian rival in a row at Melbourne Park during a rain-affected grudge match on Sunday, steam-rolling to a 6-2 6-1 victory over qualifier Maria Timofeeva.
The crushing win catapults the 21-year-old into the quarter-finals of a grand slam for the first time, and she could soon be joined in the last eight by compatriots Elina Svitolina and Dayana Yastremska.
Qualifier Yastremska has set up a fourth-round grudge match of her own on Monday against Belarusian and two-time Open champion Victoria Azarenka.
Czech surprise packet Linda Noskova stands in the way of Svitolina, the 19th seed and 2023 Wimbledon semi-finalist.
Kostyuk hopes the duo can also lock down quarter-final spots and that their success can refocus attention on the war in Ukraine, almost two years on from Russia's invasion.
Ukraine flags were visible courtside during the match between Marta Kostyuk and Maria Timofeeva. (James Ross/AAP PHOTOS)
"It really seems for a lot of people that it's over," she told reporters after the match.
"I hope that the girls can keep on doing what they're doing and reminding as much as possible.
"I had a very long break because I finished my season in Beijing, and I only restarted in Brisbane. I was out for almost three months.
"When I came back, I was, like, 'wow, OK, everyone is back to normal life like nothing happened ever' ... it's not right."
Kostyuk sent a shot across the bow after battling past Russian Elina Avanesyan in the third round, questioning why Russian and Belarusian players were allowed to compete at Melbourne Park.
She may have put a target on her back with the remark, but insisted she did not feel the pressure of the moment on Sunday, despite struggling for sleep since her marathon second-round victory over Belgian Elise Mertens.
Even when rain momentarily stopped the match on Kia Arena while she was leading 2-0 in the first set, Kostyuk didn't lose her composure.
A rain delay couldn't stop Marta Kostyuk from beating her Russian opponent at the Australian Open. (James Ross/AAP PHOTOS)
"We had this rain delay, and I spoke to (coach) Sandra (Zaniewska) for a little bit, and I said, 'you know, I'm on this court, and I don't even feel like I'm playing fourth round'," she said.
"I managed to separate completely the idea that it's a match for the quarter-final of a grand slam."
Although she won the 2017 junior singles title and reached the third round in her grand slam debut the following year, Melbourne Park hasn't always been a happy hunting ground for Kostyuk.
She failed to progress through qualifying in 2019 and 2020, and bowed out to Russian Veronika Kudermetova in the first round in 2021.
But Kostyuk still considers this her favourite tournament, revelling in the support of Melbourne's Ukrainian contingent.
She will be counting on it on Tuesday when she comes up against red-hot American fourth seed Coco Gauff, but she is keeping her expectations in check ahead of the match-up.
"I have nothing to lose really," Kostyuk said.
"I'm in my first quarter-final. She's a top-five player. I just want to go out there and really play aggressive."
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