Hee Young Park fired a three-under par 68 to claim a one-stroke lead at the rain-affected LPGA Kingsmill Championship.
The South Korean star's 36-hole total of eight-under 134 left her narrowly ahead of American pair Stacy Lewis and Brittany Lang.
Lewis completed a six-under par 65 and Lang carded a 67 but there were 24 groups left to complete their second round, including players who could challenge for the halfway lead.
Spain's Azahara Munoz and Americans Lexi Thompson and Lizette Salas also sat on seven-under when darkness halted play - Thompson and Munoz have five holes to complete and Salas seven.
The start of the round was delayed more than three hours after a storm dumped an inch of rain on the course.
But Park coped admirably with the conditions, and she said the rain-softened greens were actually easier to play after a round that included four birdies and a bogey.
"This golf course, the hardest thing is the greens are pretty firm," Park said. "But today after rain, they're holding pretty well, so a lot of players can play more aggressive.
Lewis thought it was an advantage to tee of knowing she'd complete her round, and she expects the course to be in great shape for the weekend.
The American had six birdies without a bogey. She said her closest call was at the eighth hole, where she ran a birdie attempt five feet past the hole but made it coming back.
"I definitely have a better feeling coming off the course today," said Lewis, who could claim the world No 1 spot from Inbee Park this weekend.
"I just feel like I played a lot more solid, hit the ball better, definitely had more control going into the greens.
"I think less wind helped there. I just stayed really patient and made a few putts and added up to a pretty good score."