Cincinnati - Defending champion Karolina Pliskova won twice in one day for the third time this season, tightening her grip on the world number one ranking on Friday to reach the WTA and ATP Cincinnati Masters semi-finals.
The 25-year-old Czech, fighting to hold off Romania's Simona Halep atop the rankings, first ousted Italian qualifier Camila Giorgi 6-3, 4-6, 6-0 in one of five matches postponed from Thursday due to rain.
With only two hours between matches, Pliskova defeated Denmark's fifth-ranked Caroline Wozniacki 6-2, 6-4 to book a Saturday semi-final against Wimbledon champion Garbine Muguruza.
"I feel pretty good," Pliskova said. "I recover well, so definitely I will be ready for tomorrow."
The only one of four rivals who could have toppled Pliskova this week still with hope is second-ranked Halep, who ripped British seventh seed Johanna Konta 6-4, 7-6 (7/1) to book a semi-final date with US wildcard Sloane Stephens.
"Whatever comes I will just take it," said Pliskova. "Even if I would be second coming to the US Open, it's still better than I was last year. So no pressure about being world number one."
Pliskova's two-in-one effort, matching feats on her way to Eastbourne and Doha titles, means Halep must capture the crown to swipe the top spot in Monday's rankings.
"Not always is it going this way," Pliskova said of her twin wins. "It's just lucky that I always won both of them."
Halep squandered five match points but dominated the tie-breaker for her first career victory in four tries over Konta.
"I gave everything I had. I did pretty well in the tie-breaker," said Halep, whose 4-2 record against Stephens includes a twin two weeks ago at Washington.
Ukraine's fourth-ranked Elina Svitolina lost her chance at number one when she fell 7-5, 6-4 to Germany's Julia Goerges, who then lost to Stephens 6-1, 7-6 (7/3).
Also doing double duty at the final major tuneup for the US Open was Spain's Rafael Nadal, assured of moving into the world number one ranking on Monday for the first time since July 2014.
Nadal beat compatriot Albert Ramos-Vinolas 7-6 (7/1), 6-2 to reach a quarter-final later against Australian Nick Kyrgios.
Kyrgios, ranked 23rd, outlasted Croatia's Ivo Karlovic 4-6, 7-6 (8/6), 6-3, while Austria's eighth-ranked Dominic Thiem was upset 6-3, 6-3 by Spaniard David Ferrer, who will face Nadal or Kyrgios in the semi-finals.
Both Nadal and Ramos-Vinolas wore black ribbons on their shirts in memory of victims of the terror attack Thursday in Barcelona.
"What happened yesterday in Barcelona was, of course, terrible. Everyone is very, very sad. I don't have words to say, because when these kind of things happen, is difficult," Nadal said.
"All my support to Barcelona and especially to the people that are suffering a lot, for all the families of the victims. Just keep going and sorry for everything."
Nadal, a 15-time Grand Slam champion who won his 10th French Open title in June, clinched dethroning injury-idled Andy Murray atop the rankings when Roger Federer withdrew from Cincinnati with a back injury.
Sixth-ranked Spaniard Muguruza 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."
Muguruza displayed a black ribbon on her visor in memory of Barcelona victims.
"I had it on my mind," Muguruza said.
Pliskova is 6-1 all-time against Muguruza, dropping only the first meeting in the 2015 French Open first round.
US 14th seed John Isner fired 25 aces in beating American wildcard Jared Donaldson 7-6 (7/4), 7-5 to book a semi-final with Bulgarian seventh seed Grigor Dimitrov, who downed Japan's Yuichi Sugita 6-2, 6-1.
Results on Friday from the WTA and ATP Cincinnati Masters tournament (x denotes seeding):
Grigor Dimitrov (BUL x7) bt Yuichi Sugita (JPN) 6-2, 6-1
John Isner (USA x14) bt Jared Donaldson (USA) 7-6 (7/4), 7-5
David Ferrer (ESP) bt Dominic Thiem (AUT x3) 6-3, 6-3
Nick Kyrgios (AUS) bt Rafael Nadal (ESP x1) 6-2, 7-5
Nick Kyrgios (AUS) bt Ivo Karlovic (CRO) 4-6, 7-6 (8/6), 6-3
Rafael Nadal (ESP x1) bt Albert Ramos-Vinolas (ESP) 7-6 (7/1), 6-2
Garbine Muguruza (ESP x4) bt Svetlana Kuznetsova (RUS x8) 6-2, 5-7, 7-5
Karolina Pliskova (CZE x1) bt Caroline Wozniacki (DEN x6) 6-2, 6-4
Sloane Stephens (USA) bt Julia Goerges (GER) 6-1, 7-6 (7/3)
Simona Halep (ROM x2) bt Johanna Konta (GBR x7) 6-4, 7-6 (7/1)
Karolina Pliskova (CZE x1) bt Camila Giorgi (ITA) 6-3, 4-6, 6-0
Julia Goerges (GER) bt Elina Svitolina (UKR x5) 7-5, 6-4
Sloane Stephens (USA) bt Ekaterina Makarova (RUS) 2-6, 6-3, 6-4