Park stands at 4-under-par 138 and will have a chance to pick up her third LPGA victory on Sunday after the decision was made to shorten the event to 54 holes.
The weather held up Saturday, and Sorenstam, one week after missing the cut for the first time in four years, took advantage by matching Park's 67 to get to 3-under-par 139.
'Obviously I'm happy. I get to play Sunday and that's a good thing,' said Sorenstam, before joking, 'I've improved from last week.'
Allison Hanna tied Park for the lead, but bogeyed two of her final three holes to end the day alone in third place at 2 under after a 71.
Laura Diaz, Helen Alfredsson, Seon Hwa Lee, Hee-Won Han and Juli Inkster share fourth place at minus-1.
One shot further back, Natalie Gulbis leads a group tied for ninth place at even-par. Gulbis held the first-round lead, but struggled late on Saturday and shot a 3-over 74.
Lorena Ochoa, the second-ranked player in the world, is also at even-par after her second consecutive 71.
Defending champion Paul Creamer was even-par on the day and stands in a tie for 12th place with five others. Creamer became the youngest winner on the LPGA Tour in 53 years when she broke through here last year.
Park's last LPGA win came at the 2002 Sybase Classic when she was still known as Gloria Park. Currently ranked 43rd in the world, Park is without a top-10 finish in nine previous starts this season.
'I [haven't] had a good year so far,' Park admitted. 'It was kind of slow. Since I got here, I have a good memory and I feel good about it. So maybe I have extra confidence in my game, more focus.'
That confidence showed up early in her round when Park, who began on the back nine, knocked short irons within three and 20 feet to set up birdies at the 12th and 13th holes, respectively.
That moved the 26-year-old Korean to minus-2, and she moved further into red numbers with a 10-foot birdie putt at 16. Park three-putted from 30 feet to bogey the 18th, but got that shot back and more with consecutive birdies at Nos. 2 and 3.
She moved as low as 5 under with a 15-foot birdie putt at the eighth, then gave another stroke back after coming up short of the green with her approach at the ninth.
Park tied for second last year when she missed a birdie putt at 18 and Creamer made a 17-footer for the win. She still thinks about the missed opportunity.
'I thought 'This is the hole, I need to make it.' But I didn't.' Park said.
After not making the cut last week at the Michelob Ultra Open -- her first missed cut since the 2002 Women's British Open -- Sorenstam has played steadily this week, although not spectacular.
She opened with a 1-over 72 in the first round Thursday, then followed that with five birdies and one bogey in the second round.
When she was on her game Saturday, Sorenstam was knocking shots stiff. She hit short irons within three feet at the sixth and four feet at the ninth to set up her first two birdies. But the world No. 1 also found trouble at the eighth, hitting the rough and a bunker on the way to a bogey.
Park came from behind to defeat Sorenstam for her Sybase victory in 2002, with Sorenstam finishing one shot shy of making the playoff.
'I haven't thought about that,' Sorenstam said. 'I am more focusing on my own game.'
The cut line fell at plus-8, with 71 players moving on to the final round Sunday.