Trailing 2-4 in the third set of her third-rounder, two-time Cincinnati runner-up Angelique Kerber clawed back to edge Jelena Ostapenko, 4-6, 6-2, 7-5, after one hour and 56 minutes.
In a battle of past event champions, top seed Daniil Medvedev defeated Grigor Dimitrov, 6-3, 6-3, for his third straight win over the Bulgarian.
Olympic bronze medalist Pablo Carreño Busta toppled No. 9 seed Hubert Hurkacz, 7-6 (6), 7-6 (3), to set a quarterfinal clash with Medvedev.
World No. 1 Ash Barty blitzed defending champion Victoria Azarenka, 6-0, 6-2, breaking the No. 14 seed five times to get the better of her for the second time in 2021 (Miami).
Eighth seed Casper Ruud served up a 6-4, 6-3 victory over No. 10 seed Diego Schwartzman to avenge last year’s Western & Southern Open loss when the event was held in Queens.