Jannik Sinner and Iga Swiatek stage Cincinnati fightbacks as Alex Zverev escapes
Sinner prevented rival Andrey Rublev from repeating a triumph from last Saturday in Montreal as he defeated the sixth seed in a 4-6, 7-5, 6-4 fightback.
Swiatek did the same in the women's draw as she worked to overcome teen Mirra Andreeva 4-6, 6-3, 7-5.
Sinner will square off in the semis against third-ranked 2021 champion Alexander Zverev, who got past rain interruptions in the final set to defeat Ben Shelton 3-6, 7-6(3), 7-5.
The third set was start-stop but the German advanced to his third consecutive Cincinnati final-four spot.
"Conditions and the interruptions were tough, but Ben was the toughest part of the match," Zverev said.
"He has played amazing tennis all week. It was tough to find my comfort zone today, but it's great to get the win."
In the bottom of the draw, Frances Tiafoe will play Holger Rune.
The American advanced 6-3 after half an hour when fifth seed Hubert Hurkacz who underwent knee surgery a month ago, had to retire with a calf injury.
"At 2-2 I felt he was a little off," said Tiafoe, who claimed his 200th Tour match win. "I know how it feels dealing with pain, rehab... he did come back pretty quick."
Rune, who had never won a match here until this week beat Briton Jack Draper 6-4, 6-2 in 75 minutes.
Rune broke twice in the second set to take the win in 75 minutes.
"The scoreboard was not how the match felt," Rune said. "It was very difficult, Jack was going after it," he said.
Top seed Sinner took to the court for only his second match of the week after a first-round bye and a walkover on Friday.
Sinner - whose fitness has been compromised in recent months by a hip niggle, illness and tonsillitis which forced him to miss the Olympics - stormed back to win the second set and break Rublev to start the third.
He clinched victory in a set where five of the 10 games were breaks of serve. His match-point ball was caught by a gust of wind and put out of the reach of his opponent.
"There was a lot of mental strength required today," Sinner said. "It was tough conditions, very, very windy," he said.
Sinner ended with 31 winners, including 10 aces, while Rublev, the runner-up at Montreal, committed 47 unforced errors.
Poland's Swiatek grabbed a break in the penultimate game of a match lasting more than two and a half hours to finally advance past Andreeva at the US Open tuneup, which concludes on Monday.
Swiatek moved through on her first match point, her opponent driving a return long, and won a 30th match this season at the WTA 1000 level. She stands 53-6 for the season and has won 25 matches on hardcourt.
Sabalenka advances
Swiatek will bid for the finals in Sunday's match against Aryna Sabalenka, a 6-3, 6-2 winner over Liudmila Samsonova.
Sabalenka, who has reached her fourth Cincinnati semi-final - and third in a row - will take over the WTA second-ranking spot from Coco Gauff heading into the US Open, which starts on August 26th.
Sabalenka is working to win her first title since repeating as Australian Open champion last January in Melbourne.
American sixth seed Jessica Pegula worked for more than three hours in the wind to defeat Canada's Leylah Fernandez 7-5, 6-7(1), 7-6(3) to reach the semis.
Pegula played two matches on Friday and admitted this final effort was a strain as she reached her ninth semi in the 1000 series.
"I was tired today, but I toughed it out. She started playing really well. She's a great competitor but I got fired up in the third set and settled down.
"We had really tough conditions, the wind was really swirling and we both had trouble on serve. It was crazy today but I got through."
Pegula's opponent will be Paula Badosa, who thumped Anastasia Pavlyuchenkova 6-3, 6-2.