MASON, Ohio -- Top-ranked Iga Swiatek survived in her return to hard courts Wednesday night in the Cincinnati Open, outlasting Varvara Gracheva 6-0, 6-7 (8), 6-2.
Playing for the first time since finishing third for Poland in the Paris Olympics on clay, Swiatek set up a third-round match against Marta Kostyuk -- a 6-3, 7-5 winner over Lulu Sun.
"For sure, the transition is probably the hardest, from like the slowest surface to the fastest surface," Swiatek said. "But that's why I'm still happy with my performance and looking forward to another match to kind of still do the grinding and implement what I was working on, but not really focusing on the results."
Swiatek won her third straight French Open title in May and has six WTA Tour victories this season.
On the men's side in the US Open tuneup event, top-ranked Jannik Sinner got past American Alex Michelsen 6-4, 7-5 in his first match. In the late match, Jiri Lehecka upset fourth-seeded Daniil Medvedev 7-6 (2), 6-4.
Earlier in women's play, 17-year-old Mirra Andreeva beat 11th-seeded Emma Navarro 6-2, 6-2. Andreeva was playing her first match since taking a silver medal in doubles in Paris.
"I just went out there, tried to show my best level and tried to win a match, and I think I did it," Andreeva said.
Andreeva will face 2016 Cincinnati champion Karolina Pliskova.
Toronto semifinalist Diana Shnaider of Russia, Andreeva's doubles partner in Paris, beat Zhang Shuai 6-1, 6-4.
Sinner improved to 25-2 on hard courts this season and advanced to a third-round meeting with Australia's Jordan Thompson. Sinner is trying to reach the quarterfinals in Cincinnati for the first time.
"I'm very happy to be in the next round," the Italian star said. "For me, this is a place where I used to struggle a lot in the past years, so let's see what I can do this time."
Thompson beat Sebastian Baez 6-2, 6-4.
Stefanos Tsitsipas, in his first tournament since announcing he would no longer be coached by his father, rallied to beat Jan-Lennard Struff 4-6, 6-4, 6-3.
Tsitsipas, the No. 9 seed, revealed that Apostolos Tsitsipas would no longer coach him after losing to Kei Nishikori in his first match last week in Montreal.