Yim and Kang hold a one-stroke advantage over Rosie Jones and defending champion Hee-Won Han at Columbia Edgewater Country Club. Laura Diaz, Wendy Doolan and Aree Song share fifth place at 6-under-par 66, while six players are one stroke further back in a tie for eighth place.
Rookie Yim posted a career-best score with a bogey-free round, collecting six birdies over the front nine and two on the back. She moved to 5 under through just seven holes after stringing together four consecutive birdies from No. 4.
'I feel really good today,' said the 21-year-old. 'My shot [was] really perfect today, so, I mean, not much missed today. I played really easy.'
After a birdie at the ninth put her at minus-6 around the turn, Yim moved to 7 under with another birdie at the par-5 10th. She added a birdie at No. 12 before closing her round with six straight pars to remain at 8 under.
'I was thinking, just do my best and just have fun,' Yim said. 'Not too much thinking over this tournament...I just don't want to pressure myself. It's very important to me, but I didn't think about it a lot.'
Kang started on No. 10 and opened with consecutive birdies at her first two holes before stumbling to a bogey at the par-5 12th. She birdied two more holes on the back-nine before her second bogey of the day put her at 2 under around the turn.
The 29-year-old then exploded for red numbers on the front nine, playing her final nine holes at 6 under par.
Birdies at the first, third and sixth moved Kang to minus-5, but it was an eagle at the par-5 seventh that set her up to take a share of the lead. On that hole, she struck a 3-wood within 3 feet to set up a short putt.
'I'm so happy to get a nice score today,' said Kang. 'Actually, this is my third year in the Safeway Classic. Every year I was good on this course...I think this year will be the best of years.'
All in all, a total of 30 golfers are within five strokes of the leaders heading into the weekend.