Naomi Osaka punched her ticket to the Western and Southern Open quarterfinals for the second consecutive year by defeating Dayana Yastremska 6-3, 6-1 in New York on Tuesday.
The fourth-seeded Osaka fired eight aces and saved all five break points she faced against the 20-year-old Ukrainian, who is working with Osaka's former coach Sascha Bajin, in the 70-minute match.
"I wasn't really nervous and I was able to enjoy the match," Osaka said.
"I haven't reached the level of play that I want to yet but I'm getting there," she said.
Osaka will next face 20th-ranked Anett Kontaveit for a place in the semifinals. The Japanese star has a 3-0 record against the Estonian with their most recent meeting a walkover in 2019 in Stuttgart.
Osaka failed to defend her title at the Australian Open in January, her last tournament before the tour's five-month shutdown.
She split with Bajin in February 2019 after the German coached her to back-to-back Grand Slam titles at the U.S. Open in 2018 and Australian Open in 2019.
The Japanese pairing of Shuko Aoyama and Ena Shibahara was unable to emulate Osaka in reaching the quarterfinals, with the women's doubles team losing in two sets to Americans Jessica Pegula and Shelby Rogers.
The Western and Southern Open, also known as the Cincinnati Open, is being held at Flushing Meadows in New York, the home of the U.S. Open, because of the coronavirus pandemic. The U.S. Open, which starts Aug. 31, is set to follow the WTA Premier 5 event.