And as the boilovers kept coming at Roland Garros on the second Sunday, the prospect of the 2026 victor being the first ever Ukrainian grand slam singles winner also grew with Elina Svitolina continuing her hot form to reach the quarter-finals.
Arguably, the only disappointment for the Ukrainian challenge was that Madrid Open winner Kostyuk and Italian Open champ Svitolina, who've both been stand-outs on the clay-court circuit over the past month, must play each other in the quarter-finals.
Svitolina didn't see it that way, though. "There's going to be Ukraine in the semi-finals, so it's already amazing," she beamed after rallying past former Olympic champ Belinda Bencic 4-6 6-4 6-0.
"It couldn't be a better, more amazing achievement for Ukrainian tennis. In such a difficult situation right now in the war, with the (Russian) invasion, it's really, really difficult, and it's really inspiring for the next generation to really believe that it is possible one day to play on this court and win."
Kostyuk, eight years the junior of 31-year-old Svitolina, enthused: "It's such an honour to share the court with her. She's paved the way for a lot of Ukrainian girls and boys, and she's doing great, this year unbelievable. So excited for this match."
A day after women's champion Coco Gauff had crashed out and hot on the heels of the exit of men's giants Jannik Sinner and Novak Djokovic, third seed Swiatek admitted she had got "super tense" as she was simply swept aside in her fourth-round clash 7-5 6-1 by Kostyuk on Court Philippe Chatrier.
After two title wins already this clay-court season in Rouen and Madrid, Kostyuk reeled off a 16th successive victory on the circuit.
Swiatek's birthday celebrations really went sour after she had succumbed in a tight first set, during which the pair twice traded breaks, as the 15th seed Kostyuk then saved three break points to move 2-1 ahead in the second stanza and took complete control.
She lost just three more points in the last four games, hitting a purple patch that left the Pole powerless with a host of searing winners - 25 in all over the one-hour 39-minute contest.Â
It was another huge day for 36-year-old Romanian veteran Sorana Cirstea, who's planning to retire at the end of the season but who's clearly got some unfinished business first as she beat Chinese qualifier Wang Xiyu 6-3 7-6 (7-4) to reach her second Roland Garros quarter-final -- 17 years after her first.
The gap between those last-eight appearances in Paris is the longest at a single major by any woman in the Open Era.
"There is no expiration date for ambition and for dreams," Cirstea told the crowd. "I think back then I was a kid, just started on tour. Now I have so many years behind me. I have so much experience, maturity. I feel I'm a completely different player."
The veteran will meet eighth seed Mirra Andreeva, who after a merciful spell of rain cooled off Roland Garros following its boiling week, defeated Swiss Jil Teichmann 6-3 6-2.
