Lorena Ochoa, a co-leader after the second round with Park, carded a 1-over 72 on Saturday and is tied for third with Hee-Won Han (66) and Suzann Pettersen (71). The trio is 6-under-par 207.
The sport's top two stars are part of group tied for sixth. Annika Sorenstam and Se Ri Pak posted matching rounds of 1-under 70 and share sixth place with Nabisco Championship winner Patricia Meunier-Lebouc at minus-5.
'I played pretty well, but I felt like I didn't get the most out of my round,' Sorenstam said. 'For three days I've been grinding and grinding. I've just been very close.'
Park did not get off to a great start on Saturday as she landed her tee ball at the par-3 second in a bunker. She blasted out to 10 feet but could not convert the par save. Park made up for the miscue at two with a two-putt birdie from 60 feet at the par-5 third hole.
Park found more trouble at the next par-3, the 170-yard fifth. Her tee shot landed in water but her third found the green. Park could not convert the bogey putt so she left with a double bogey and she fell out of the top spot.
'Nobody goes right at the flag,' said Park, referring to the fifth hole. 'I was aiming it a little left. I hit two clubs longer than I should have and choked down too much and tried to swing it easy and ended up blocking it way right.'
Park recovered at the par-5 seventh with a five-foot birdie putt, but her play on the back nine at Kingsmill Resort & Spa sent her to the top of the leaderboard. She knocked a sand-wedge to 12 feet to set up birdie at the 11th and reached the par-5 15th in two to record her second birdie of the back nine.
At the 18th, Park found herself tied with Kerr in first at 8-under par. She played a 9-iron 20 feet short of the hole and sank the birdie try to take her first 54-hole lead since the 2001 Office Depot.
'Starting out the round I could not hit the green to save my life,' said Park. 'I don't get to play in the lead very much so I will take what I have right now. As long as I stay ahead of whoever is right behind me, I win.'
A win on Sunday would be Park's first of 2003 and her fourth since joining the LPGA Tour in 2000.
Kerr did nothing spectacular on Saturday but played steady with three birdies and no bogeys. She holed a 10-footer for birdie at the third and tallied her second birdie of the front nine with an up-down birdie at the par-5 seventh.
Kerr took sole possession of the lead at the 16th when she knocked a 5-iron to 70 feet and drained the long birdie putt. It wasn't until Park upstaged her at 18 that Kerr fell into second place.
'I played really well today,' said Kerr, who won the Longs Drugs Challenge last year. 'I have not hit the ball great all week and I have been getting up and down quite a bit.
'You have just got to hit it in the right spots on the greens. I feel good going into tomorrow. I don't know if I am going to hit it any better, but obviously it's been working so far.'
Karrie Webb (68), Laura Davies (68), Meg Mallon (70) and Mi-Hyun Kim (71) share ninth place at 4-under-par 209.