Dottie Pepper and Mi Hyun Kim each carded rounds of 4-under-par 67. They share third place with Carri Wood and Heather Bowie.
Diaz had a rough start at Highland Meadows Golf Club. She opened on the 10th hole and promptly three-putted for bogey. After settling down to par the next three holes, Diaz got back to even-par when she dropped in a four-foot birdie putt on the 14th.
She closed out her opening nine in fine fashion. The 28-year-old drained a 60- foot birdie putt at the 16th and followed that with a 12-foot birdie at the next.
At the par-5 18th, her ninth, Diaz dropped a sand-wedge within nine feet and sank that birdie try to close with three consecutive birdies.
Diaz turned the triple again on the front side. She converted a seven-footer for birdie at the third and birdied the next two holes to climb to 6 under.
She nearly holed her third shot to the par-5 seventh, but the ball stopped one foot from the cup for a kick-in birdie. After missing the fairway at her last, No. 9, she was unable to get up-and-down to save par to end with a one-stroke advantage.
'It feels good to shoot under par again,' said Diaz. 'I've had a little bit of a struggling year, so it's nice to post a low number. I putted really well today, and I'd have to say that was the key. I made two huge putts, one that was probably 60 feet and another one that was 35 to 40 feet.'
Diaz has been battling an old ankle injury for most of the season and it has affected her game.
'My doctor said I had a tear in the peroneal tendon, which is the tendon that runs on the outside of your ankle bone,' Diaz said. 'He believes it was caused from a sprain in my junior year in college. I've been going to a massage therapist. He's used electronic acupuncture and deep-tissue massage to help the heeling process.'
Teske, who has two wins to her credit this season, also began on the back nine Thursday. She started quickly with a birdie at her opening hole. At the par-3 14th, Teske dropped a 4-iron within 10 feet to setup her second birdie. At the par-5 17th, she again sank a 10-footer for her third birdie of the round.
Around the turn, Teske dropped a 5-iron within five feet at the first to setup birdie. She followed that up with another birdie at the next to move to minus-5.
Teske, however, could not maintain that momentum. She missed the fairway at No. 4 and was unable to save par. She did get that stroke back at the seventh when she sank a five-footer for birdie.
'I hit the ball really solid and made birdie on the first hole,' said Teske. 'It started from there and I got a little bit of momentum. My putting felt really good, and I felt confident out there.'
Meg Mallon and Hee-Won Han both posted rounds of 3-under-par 68. That duo shares seventh place with Paula Marti, Jill McGill, Joanne Morley, Fiona Pike, Jenny Rosales, Nancy Scranton, Marisa Baena, Nicole Jeray and Kelli Kuehne.