Mi Hyun Kim and overnight leader Tina Barrett share third place at 4-under-par 140. Soo-Yun Kang, Se Ri Pak and Grace Park are one stroke further at minus-3.
Teske began her day two strokes off the lead at Locust Hill Country Club. She birdied the third from six feet and rolled in a 20-footer at the fifth to move to minus-5.
Around the turn, Teske stumble to her lone bogey of the day at the par-4 10th. Teske birdied the par-4 12th to get back to 5-under. She followed the with a three-foot birdie putt at the next and made it three in a row when she drained a 20-footer for birdie at the par-4 14th.
'I hit the ball pretty solid today,' said Teske. 'I kind of tried to swing within myself because I kind of stretched this morning and walking back to the clubhouse I felt a bit of a twinge in my rib again.'
Teske first injured the rib in 1998 and has occasionally felt twinges over the last three years.
'I didn't really want to push it too far,' Teske said. 'It didn't really hurt to swing or anything so I just kind of teed off and wanted to see how it would go.'
Teske is in a hot stretch right now. She tied for eighth at the McDonald's LPGA Championship two weeks ago and won the Giant Eagle Classic last week.
'I hit a patch I guess. In 1999, I won the Chick-fil-A and the week after I won the tournament in Myrtle Beach,' said Teske. 'I tend to play good in runs I guess.'
Eathorne, for the second straight day, had an up-and-down back nine. She started with a bogey at her first hole, No. 10 but she erased that mistake with a birdie at the 12th from six feet.
She dropped another shot at the par-3 15th when she was unable to get up- and-down. Eathorne followed that with back-to-back birdies from the 16th. However, she was unable to maintain that momentum as she bogeyed the 18th to make the turn at even-par for her round.
'I actually started with a bogey and I wasn't really hitting it too super well to start with,' said Eathorne. 'I managed to get through the spot where I hit sort of a bump in the road Thursday on the back side and got through the holes at 1-under. I had another bogey on 18 but I think that was more nerves than anything.'
On the front side, she picked up a birdie at the second when she dropped a wedge within seven feet before parring out to remain in second place.
'I felt stronger out there today,' Eathorne said. 'I didn't score well but I putted pretty well. I saved a lot of shots on the second nine where I was off a little bit and made 10- and 12-footers for par that might not have gone in yesterday but I feel really good over the putter right now.'
Silvia Cavalleri, Wendy Doolan and Marianne Morris are tied for eighth place at 2-under-par 142.
Defending champion Karrie Webb finished two rounds at 1-over-par 145, which was three strokes better the 36-hole cut line of 4-over-par 148.