Lee is 8-under and sharing second after a stunning round of golf while Oh is two shots further back and sharing fifth after some fireworks of her own.
American Marina Alex leads the tournament after a 10-under 62, her advantage two shots over Lee and last week’s winner Brooke Henderson.
Little known American Robyn Ree is fourth alone at 7-under with Oh and British Open champion Georgia Hall at 6-under.
Hannah Green is 3-under and T24, Katherine Kirk and Rebecca Artis 2-under and T42 while Sarah Jane Smith is 1-under and T64 on a day of low scoring.
Lee was out in the early pairings and teeing off the 10th set the course alight early with five straight birdies to open her account.
Another birdie at 16 had her out in 6 under 30 and threatening something extraordinary but she cooled on the inward half.
Three birdies against a lone dropped shot for the day at her final hole was hardly poor play but after her fast start looked a little pedestrian.
Lee, rightly, didn’t see it that way saying after the round she was confident in all parts of her game.
More ==> pic.twitter.com/kTDl1rwkB8— LPGA (@LPGA) August 30, 2018
“With an 8-under today I'm pretty confident with pretty much all aspects of my game,” she said after signing her card.
“I had a really fast start. I think I made five birdies in a row. Nice start on the back nine. I was really hitting it close.
“Hopefully I can follow it up with a good round tomorrow.”
Lee has had a remarkably consistent year with a victory and 10 top 10 finishes in 20 starts to date.
Oh has had a less impressive 2018 resume though in recent weeks has shown signs of improving form.
She parlayed a T4 result last week in Canada into a fast start of her own in Oregon with a birdie at her opening hole and three straight to close out the nine.
A fourth on the trot was the ideal start to the back nine and after adding two more against a lone dropped shot she is well in the mix.
Leader Alex was also out early and bogey free in her 10-under effort, a blistering finish icing on the cake of an otherwise good day.
Out in 4-under she added two further birdies at 10 and 13 before streaking home with four straight from the 15th.
Yet to win a Tour event, Alex has been a steadily improving performer in 2018 with three top five results to date though expects there to be plenty of competition if she is to claim a maiden title this week.
“I'm sure the scores are going to be pretty low this afternoon,” she said after her round.
“The course is in perfect shape. So if you're hitting your lines you're going to make a ton of putts.
“I'm sure tomorrow 10-under probably won't even be close to the lead when I tee off. I'm going to have to come out and make as many birdies as I can the next three days.”
MINJEE LEE - WHY I LOVE GOLF:
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