Choi shot a 5-under 67 to tie the 28-year-old American at 14-under 202. Lewis, the overnight leader and reigning LPGA Player of the Year, had a 69.
Paula Creamer, who injured her shoulder in a car accident after a tournament in Thailand last weekend, shot 69 to trail the leaders by two shots.
Four golfers were three strokes behind Creamer — American Danielle Kang (70), Spaniard Azahara Munoz (72), South Korean Sun Young Yoo (72) and Thai 17-year-old Ariya Jutanugarn (72).
Lewis and Choi were in the last group on the course and had just teed off on the 18th when a thunderstorm rolled in and caused a 2½-hour delay. Lewis was up a stroke when they left the course, but when they returned, Choi made a 10-foot birdie putt to pull even heading into Sunday.
The two golfers traded the lead throughout the day. Lewis bogeyed holes No. 1 and 3 to fall two strokes behind Choi. Lewis pulled even after reeling off three straight birdies — including a 25-foot putt on No. 8 that barely caught the edge of the hole.
Choi moved atop the leaderboard again with a birdie on the 14th, but she bogeyed the next hole after missing a long par putt to give the lead right back.
Lewis maintained the one-shot advantage going into the 18th. And then the rain came.
“It was very frustrating,” Lewis said. “It is what it is and luckily we got finished today. It’s going to be tight tomorrow and we are going to have to make some putts.”
Creamer, who was in the next-to-last group, said she barely made it off before the start of thunder and lightning.
“Sometimes it has its perks being second to last,” she said. “Dinner will taste a lot better, especially not having to grind it out on the last hole.”
Creamer, the 2010 U.S. Open champion, had low expectations coming into the tournament after injuring her shoulder in a five-car accident on the way to the Bangkok airport on Sunday night.
She said the pain was so bad Thursday morning that she wasn’t sure if she’d play.
“I’m just so pleased to be out here, and let alone to be in contention on Sunday,” Creamer said. “That’s just beyond my imagination of what I thought even teeing it up on Thursday.”
Top-ranked Yani Tseng had a 71 on Saturday. The five-time major winner hasn’t won a tournament in nearly a year and could be in danger of losing her No. 1 spot to Choi, currently in second.
Choi can’t overtake Tseng with a victory this week, but she is moving closer.
“I think that if I think about that tomorrow, then I don’t think I can have good results,” she said. “So I will try to just think about one shot at a time.”