Andreeva is only at the start of her career – and this victory means she is the first player born since 2005 to reach a major singles final.
However, she has long been tipped for Grand Slam success, with this her second semi-final appearance at Roland Garros after a loss in 2024.
Kostyuk is the in-form player on the WTA Tour, boasting an unrivalled 17-match unbeaten streak on the clay this season.
But no player has amassed more wins on clay (21) – or indeed overall (35) – than Andreeva in 2026.
Following the shock exit of world number one Aryna Sabalenka on Wednesday, eighth seed Andreeva will believe this is her time after overcoming an opponent who had beaten her in both their previous meetings this year.
Despite the blustery conditions, Andreeva was solid from the baseline and stubborn in defence – committing far fewer unforced errors (22) than her opponent (34), who was unable to hit the heights of her emotional all-Ukrainian quarter-final against Elina Svitolina.
Having dropped only one set – in her comeback second-round win against Spaniard Marina Bassols Ribera – across her six victories so far, the nature of this performance means Andreeva will walk out as the favourite on Saturday.
“Until this match, she has not lost a match on clay. She is an amazing player and a very tough opponent, and I am super happy with the way I played today,” Andreeva said of Kostyuk.
“I told myself to accept everything that happens on the court and no matter what happens, I am going to fight and give my best.
“With this kind of mindset, I ended up winning the match.”
