World number one Swiatek, who raised her game at the key moments, broke the Wimbledon champion five times and saved four of six break points to seal victory in 91 minutes.
"It wasn't easy to adjust to her spin because she's a lefty," French Open champion Swiatek said during her on-court interview.
"She really used that and her experience for sure but I really wanted to be determined and fight for every ball, and in the end this is what worked."
Vondrousova enjoyed an ideal start and dropped only three points on serve by the time she built a 5-3 lead and served for the set twice. But she was denied both times by Swiatek before the Pole ran away with the tiebreaker.
Swiatek found a higher gear in the second where she feasted on Vondrousova's serve and broke three times, including in the final game where she sealed the win with a forehand down the line that the Czech was unable to chase down.
Swiatek, who is using this event as a tune-up ahead of her title defence at the August 28th-September 10th US Open, credited the adjustments she made in between sets for her ability to make quick work of Vondrousova in the second frame.
"I tried to learn from that first set, and in the second set I knew exactly what to do and I think that's why it was such a good performance," Swiatek said.
Swiatek, who has occupied top spot in the world rankings since April 2022, will next face American seventh seed Coco Gauff, who defeated Italian qualifier Jasmine Paolini 6-3, 6-2.
Unseeded Czech Karolina Muchova needed just 11 minutes on court to reach the semis as compatriot Marie Bouzkova retired from their match with a right leg strain while trailing 3-0.
Muchova now faces Belarusian second seed Aryna Sabalenka, whom she beat in the Roland Garros semi-final earlier this year.
Ons Jabeur overcame Sabalenka en route to the Wimbledon final this year and their rematch had all the makings of an epic battle as they twice traded breaks in a tense first set before Sabalenka closed out the 12th game with a lethal backhand return.
Jabeur was up a break in the second set when the affair began to unravel, however, as the Tunisian took a medical timeout to have her right foot taped by a member of the tournament staff.
She bounded off her bench and jogged back onto the court but was clearly not herself anymore as she handed Sabalenka the break with a double fault in the sixth game and could not put up much of a fight as the Belarusian broke her again in the eighth.
"I'm super happy to be in the semi-finals again in Cincinnati, but right now I'm a little bit sad for Ons," the Australian Open winner said in on-court remarks.
"Fingers crossed - (Muchova is) a great player, we had really great battle at Roland Garros."
