Those three were the only ones under par after two rounds at the Prairie Dunes Country Club as the winds kicked up Friday to turn the course into a severe test.
The difficult playing conditions got the best of two-time defending champion Karrie Webb of Australia, who missed the cut for only the fourth time in her LPGA Tour career.
There were just four sub-par scores posted at Prairie Dunes Friday and Sorensteam had one of them -- a 1-under 69. Inkster and Diaz both shot a 72 to leave them tied with Sorenstam at 1-under 139.
Sorensteam, a two-time winner of this event, birdied four holes on the front nine to storm into contention.
The co-leaders had a one-shot advantage over Michele Redman and Australian Shani Waugh, who was tied for the lead after one round. Another shot back at 141 was Jill McGill. Among those still in the chase was Sorenstam's sister, Charlotta, who shot a 70 Friday for a 143 total.
It took a score of 9-over 149 to make the 36-hole cut and Webb wound up at 152 for two rounds. She became the first defending champion to miss the cut since Alison Nicholas in 1998.
"I'd have to dig so far into my subconscious to find blame," Webb said. "I've always done well under pressure. That was the biggest shock yesterday (when she shot a career-worst 79). This wasn't a very good couple of days."
Friday's round was also likely the last in a Women's Open for Nancy Lopez. She announced earlier this year she will be leaving the tour.
Lopez shot a 160 for two rounds and received a standing ovation from the crowd around the 18th green when she finished.
After receiving hugs from playing partners and fellow Hall of Famers Patty Sheehan and Betsy King, Lopez had to wipe tears out of her eyes as she walked off the green.
"I knew it was going to be tough," said Lopez. "I'm so grateful to the fans. That made me emotional. I want to thank the fans for all the support over the years."