Park was 10 under for the round and 20-under 193 overall, one stroke better than American Angela Stanford and two shots ahead of Scotland's Catriona Matthew.
Park nearly chipped in on the 18th hole for an eagle before tapping in a short putt for her sixth birdie on the back nine.
"I finished really well, finished (with) the birdie, so it's going to be fun tomorrow," she said.
Matthew (68) started the day with a three-shot lead on Stanford (64) but fell back with a double-bogey on the par-3 12th. She followed with a birdie and got another stroke back with a birdie on No. 18.
"Yeah, didn't maybe click quite as well today, didn't hit it quite as close," Matthew said. "Had a lot of chances but just kind of left a few, and then a silly double on 12, kind of getting a bit greedy going for the hole and just pulled it.
"Nice to come back with a couple birdies."
Meena Lee of South Korea was three shots off the lead after a 65, while Sweden's Anna Nordqvist shot a 67 and was five shots off the pace. A total of 21 players were at 10 under or better.
South Korea's Inbee Park remained in contention after a 67, good for a ninth-place tie at 13 under. Park has won her last three tournaments and is trying to become the first golfer to win four straight LPGA tournaments since Lorena Ochoa in 2008.
Nancy Lopez holds the tour record with five consecutive victories in 1978, a mark matched by Annika Sorenstam over the 2004-05 seasons.
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