Czech defending champion Karolina Pliskova tightened her grip on the world number one ranking but was preparing for a second match Friday at the WTA and ATP Cincinnati Masters.
Pliskova ousted Italian qualifier Camila Giorgi 6-3, 4-6, 6-0 in one of five matches postponed from Thursday due to rain. She faced a short-rest quarter-final against fifth-ranked Dane Caroline Wozniacki at the last major tuneup for the US Open.
The winner will advance to a Saturday semi-final against Wimbledon champion Garbine Muguruza, who ousted Russian eighth seed Svetlana Kuznetsova 6-2, 5-7, 7-5 in a matchup of two-time Grand Slam winners that lasted two hours, 45 minutes.
"It was one of the best matches of the year," Muguruza said. "It was a battle. I fought so hard. It was very tough. We both played very well."
Pliskova saved two break points and held in the final game of the first set but Giorgi hit a backhand winner on the only break point of the second set to force a third, which the Czech dominated to advance.
Romania's second-ranked Simona Halep could dethrone Pliskova from the top spot this week, but Ukraine's fourth-ranked Elina Svitolina lost her chance at number one when she was beaten by Germany's Julia Goerges 7-5, 6-4 in a third-round match.
If Pliskova beats Wozniacki, she will force Halep to win the title to seize the top spot. Halep was set to face Britain's seventh-ranked Johanna Konta in a later quarter-final. Konta has won all three of their prior matchups.
If Pliskova loses, Halep would become next week's world number one by beating Konta. But Halep has lost two prior matches this year with a chance to ascend to number one, falling to Jelena Ostapenko in the French Open final and to Konta in a Wimbledon quarter-final after having won the first set in both matches.
Goerges has a short-rest quarter-final against American Sloane Stephens, who eliminated Russia's Ekaterina Makarova 2-6, 6-3, 6-4.
Spain's sixth-ranked Muguruza displayed a black ribbon on her visor in memory of victims in Thursday's terrorist attack in Barcelona.
"I had it on my mind," Muguruza said.