Kostyuk already is the youngest player since Martina Hingis in 1996 to win a main-draw match at the Australian Open. That came after three three-set matches in qualifying over six hours.
Kostyuk is managed by Ivan Ljubicic, who works with Federer, and so gets the benefit of some first-rate analysis.
“Ivan is always helping me,” she said. Smiling, she added, “After every match, he’s telling me what’s wrong.”
Kostyuk’s progress is set to become more difficult, with a meeting against Svitolina in the next round.
While Kostyuk was playing on Margaret Court Arena, Svitolina, who won a tour-leading five titles in 2017, had a 4-6, 6-2, 6-1 win over Katerina Siniakova on the adjoining Rod Laver Arena.
Their fellow Ukrainian, Kateryna Bondarenko, beat No. 15 Anastasia Pavlyuchenkova, 6-2, 6-3, in the day’s opening match on Melbourne Park’s third show court to reach the third round here for the third time.
Zhang Shuai, who defeated the United States Open champion Sloane Stephens in the first round, was toppled by the Czech qualifier Denisa Allertova, 6-4, 7-6 (5).
On the men’s side, No. 10 Pablo Carreño Busta was leading, 6-2, 3-0, when Gilles Simon retired from their second-round match with a leg injury.
Andreas Seppi beat Yoshihito Nishioka, 6-1, 6-3, 6-4, and Gilles Muller defeated Malek Jaziri, 7-5, 6-4, 6-7 (5), 3-6, 6-2.