Cristie Kerr carded a 3-under 68 to finish at 8-under-par 134. Paula Creamer, a 17-year-old amateur from Pleasanton, California, had grabbed the lead when she finished at 8 under, before being passed by Killeen and Sergas. Creamer fired a 7-under 64 and joins Kerr in third place, one stroke clear of Mi Hyun Kim.
Killeen parred the first five holes of her round before sinking a 6-foot birdie putt at the sixth at the Marriott Sea Resort Bay Course. She then birdied the eighth from 5 feet out to get to 8 under.
The 42-year-old Georgia native caught fire down the stretch. She dropped her gap-wedge within 10 feet of the cup at the par-4 15th to set up her third birdie.
Killeen, who owns just nine top-10s in her 12 years on tour, came right back with a short birdie putt at the 16th. She knocked her second shot to 3 feet for birdie at No. 17 and two-putted for birdie on the par-5 closing hole to match the 36-hole scoring record of 130, which was set by Amy Benz in 1996.
'Today, I watched everybody else make birdies,and once again, I made a couple,' Killeen said. 'I kind of hung in there and finished with a little flurry there.'
Killeen, who has never won on the LPGA Tour, posted her best career finish in 2001 when she tied for fourth at the Longs Drugs Challenge and matched that finish later that year at the Michelob Light Classic.
'I still have my goal in front of me,' said Killeen, who played with Kerr and Sergas. 'Still have six more birdies to make tomorrow. I feel I can only control what I do, not what everybody else does.'
Sergas stuck her second shot 3 feet from the cup at the second for her first birdie of the day. She sank a 3-footer at the next and a 9-footer, both for birdie, at the fourth to climb to minus-9.
The 24-year-old missed the fairway at the eighth and that led to her first bogey. Sergas stumbled to a three-putt bogey at the 12th to slip back to 7 under.
Sergas hit a 6-iron to the par-3 14th and knocked it 4 feet from the hole. She drained that putt and two-putted for birdie at the par-5 16th to get back to 9 under. Sergas got within two shots of Killeen with a birdie at the last.
'I played with two really good players and it's fun to see good golf,' said Sergas. 'And it's fun to play good golf too. So I'm happy.'
Creamer opened at minus-1 and dropped a shot at the first with a three-putt bogey. She then rolled off five straight birdies, including two from 35 feet out.
The young Californian was unable to get up-and-down for par at the 10th, but she quickly made up for that mistake. Creamer drained consecutive birdies from the 13th and again from the 17th to jump into a share of third place.
Maria Hjorth and Joanne Mills share sixth place at 6-under-par 136. Juli Inkster, Carin Koch, Miriam Nagl, Kelly Robbins, Jenny Rosales, Sherri Steinhauer and Karrie Webb are one stroke further back at minus-5.
The cut line fell at 2-over-par 144. Defending champion Angela Stanford rallied with a 69 on Saturday, but missed the cut by one stroke at plus-3.