Competing in Australia for the first time since 2012, the 31-year-old is gunning for a 20th career win and her first on the LPGA Tour in almost two years.
She jointly held the overnight lead with Jodi Ewart Shadoff, but the Englishwoman had a horror day at the Royal Adelaide Golf Club, slumping to a four-over-par 77 to be nine off the pace.
In contrast, the stoic Park kept her momentum going with a 68, making four birdies on the front nine and three on the back to take control, including a 20-footer at the last.
It left her three clear of emerging star Cho, who is 12 years younger than her illustrious countrywoman.
American Marina Alex is a shot further back, with French pair Perrine Delacour and Celine Boutier one behind her.
"I don't think my emotions show very much but I get nervous as well. And tomorrow I will play under a lot of pressure, just like other final days in contention," said Park.
"It's going to be a fun day. I love the golf course, the way it is playing. It think it's a good competition we are going to have tomorrow."
Cho, the KLPGA Tour's Rookie of the Year in 2019, is enjoying some sparkling form on her Australia swing.
She led going into the last day of the LPGA Vic Open last weekend before the pressure told and she struggled to a final round 81.
Park said she had been impressed with the progress Cho has made.
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