The Polish star beat her former junior rival Caty McNally of America 6-4 6-4 to move within one victory of becoming the first player to win 60 matches in a single season for five years.
Caroline Wozniacki was the last player to achieve the feat in 2017.
"It was definitely physical, at the beginning of the second set I could feel my energy level went down a little bit," Swiatek was quoted as saying on the official WTA website.
"I'm pretty happy I got it back again and I could use my experience in my important moments, because Caty played really well.
"Tactically it was easier to prepare, because I know her game style. She's playing differently to other players.
"But on the other hand, a lot of time has passed since we played last time. I knew she'd made progress and I had to be ready."
Swiatek will meet Seoul champion Ekaterina Alexandrova next after the Russian's 6-1 4-6 6-1 victory over wild card Tereza Martincova.
Barbora Krejcikova booked her semi-final spot with a 7-6 (7) 6-3 victory over Alycia Parks.
The Czech, who saved a set point in the first set, will meet reigning Wimbledon champion Elena Rybakina in the last four.
Rybakina overcame Petra Kvitova 7-6 (5) 6-4 in a hard-fought contest that lasted just over two hours.
Ons Jabeur, making a rare home appearance, was upset by Claire Liu at the Jasmin Open in Tunisia.
The world number two was beaten 6-3 4-6 6-4 by Liu, who is 73rd in the world rankings.
It was the American's first career win against a top 10 player.