Cristie Kerr finished one shot off the pace at 5-under-par 67. Lorena Ochoa, Rachel Teske and Wendy Doolan followed at 4 under.
Inkster got into red figures early on under wet conditions at the Magnolia Grove Crossings Course after her second shot stopped within 6 feet of the hole for a birdie at the par-4 third. She added a birdie at the par-5 sixth and ran off back-to-back birdies starting at the par-4 10th to get to minus-4.
The 44-year-old continued her fine play down the stretch with a birdie at the par-5 16th. At the closing hole, Inkster knocked a 9-iron inside 8 feet and drained the birdie putt for her share of first.
'I haven't really played great this year. I kind of struggled with my ball striking,' said Inkster, whose best finish this year is a tie for second at Kingsmill.
Diaz was also on fire early with three birdies over her first nine holes. She carried that momentum to the inward half and kept on rolling with two straight birdies from the 11th.
Diaz hit her tee shot to 5 feet for a birdie at the par-3 14th to reach 6 under. She missed the green at the following hole but chipped within 2 feet to save par. Diaz then parred her way in to join the logjam atop the leaderboard.
'I'm just trying to go out and make as many birdies as I can,' Diaz said. 'I just want to finish out the year with some nice scores.'
Kim mixed two birdies and two bogeys on the front side to make the turn at even par. The 20-year-old made her move quickly on the back nine, starting with back-to-back birdies from the 10th.
She ran home a 10-foot putt for a birdie at the 13th and played her tee shot inside 2 feet for a kick-in birdie at the 14th. Kim then birdied two in a row starting at the 16th to post a 30 on the back side.
'I'm just really, really pleased I was able to come out here and break par in all honesty,' said Kim, who earned her first career win at this year's Longs Drugs Challenge.
Park, who has finished in the top 3 in each of her last five events including a win at the CJ Nine Bridges Classic, collected four birdies and a bogey over her first nine holes to climb to 3 under around the turn.
The 25-year-old sent her second shot into a greenside bunker at the par-5 16th but hit out of the sand to 5 feet. Park made the birdie putt and landed her tee shot within 6 feet of the hole for a birdie at the par-3 17th.
At the par-4 18th, Park dropped her approach inside 8 feet and sank the birdie putt to make it three in a row.
'I feel very good with my game,' said Park. 'This is my sixth week in a row, but I feel good with my swing, I feel confident on the greens and good things keep happening.'
Karrie Webb, Carin Koch, Sophie Gustafson, Karen Stupples, Patricia Meunier- Lebouc, Candie Kung and Heather Daly-Donofrio share ninth place at 3-under-par 69.
Defending champion Dorothy Delasin is five shots back in a group at 1-under-par 71.