Rachel Teske and Karrie Webb posted matching rounds of 5-under 67 to move into a share of third place. They were joined at 3-under-par 213 by Mi Hyun Kim, who shot a third-round 69. Grace Park also shot a 67 and is the final player under par at 2-under-par 214.
Delasin moved into the lead early on with a birdie at the first, but she settled down from there. She dropped back to minus-1 with a bogey at the par-5 fourth. As she parred the final five holes on the opening nine, she was passed by several players but came on strong on the back side.
Around the turn, the three-time winner on tour caught fire. She nearly holed her second shot at the par-4 10th, but settled for a kick-in birdie. Delasin followed with a 15-footer for birdie at the next.
'My best shot was the one on No. 10 where I knocked it within inches, so I just had to tap it in and not look at the putt and concentrate,' said Delasin. 'I was frustrated early on the front because I wasn't making any putts.'
The 23-year-old capped a run of three straight birdies when she drained a 25- footer for birdie at No. 12. Delasin later two-putted for birdie at the par-5 16th. She then moved atop the leaderboard with a 10-foot birdie putt from the fringe on the 17th.
Her birdie try at the last just slid past the edge of the cup, but the lead was hers as Han bogeyed the final hole at the Magnolia Grove Crossings Course.
'The birdie on 10 relaxed me and helped me play solidly on the back nine,' said Delasin, whose last win came at the 2001 Samsung World Championship. 'A win would mean a lot since I've been through a lot personally, including an injury. It would be a good triumph for me.'
Han began her day with four straight pars. She then posted back-to-back birdies from the fifth to move to 3 under.
The South Korean moved to minus-4 with a birdie at No. 10. She picked up her final birdie of the day at the par-5 13th to climb to 5 under.
However, her drive on the closing hole found a fairway bunker and led to a bogey to drop her into second place.
'This course is pretty narrow so you need to keep the ball on the fairway and hit the greens,' Han said. 'The greens are tough to read, but my caddie has been helping me a lot.'
Se Ri Pak, the 2002 champion, fired a 5-under 67 to climb to even-par 216. She is tied for seventh place with Laura Davies (70), Rosie Jones (71), Lorie Kane (72) and Meg Mallon (70).
Beth Daniel and Gloria Park are tied two strokes further back at 2-over-par 218.