There was little to separate the duo in the first set as they twice traded breaks, before Kostyuk took control at the end.
The brilliance of Swiatek’s strokeplay was on display when returning against Kostyuk but unforced errors hampered her serve as two double faults gave the Ukrainian the advantage before she won the opening set with a fine backhand winner.
Kostyuk had not taken a set off Swiatek in their three previous tour-level meetings and the 23-year-old’s confidence grew as she tightened her grip on the match.
Her powerful groundstrokes continued to wear Swiatek down as she ran away with the second set to reach the last eight at Roland Garros for the first time, while it is the first time that Swiatek has failed to reach the quarter-final at the French Open since her debut in 2019.
Swiatek’s defeat comes amid a spell of big names exiting the men’s and women’s draws at Roland Garros.
Men’s world number one Jannik Sinner, 24-times Grand Slam winner Novak Djokovic and defending women’s champion Coco Gauff have all gone out of the event in recent days.
Meanwhile, Romanian 18th seed Sorana Cirstea is into her second French Open quarter-final – 17 years after her first appearance in the last eight at Roland Garros.
The 36-year-old, who plans to retire at the end of the year, was a 6-3 7-6 (7-4) winner against Chinese qualifier Wang Xiyu.
