Prammanasudh had seven birdies and three bogeys and was at 10-under 134. The 18-year-old Pressel shot a 65.
Rookie Angela Park, who waited out the delay to start her round, was at 6 under along with Mi Hyun Kim (67) and Carri Wood (68). Jee Young Lee also was 6 under with 14 holes left.
The day started out with sunny conditions but the usually dry Leeward Coast was hit by a downpour just as the morning leaders stepped into the media tent. The rain soaked players, sent spectators running under coconut trees and drew a smile from the players in the clubhouse.
More than half the field waited out the rain delay. It cleared up about an hour after play was halted at 1:18 p.m., and crews busily worked to make the course playable. Play resumed at 4:19 p.m., leaving only a couple hours of daylight.
Despite being atop the leaderboard, Prammanasudh (pronounced PRAH-mahna-sood) wasn't happy with her round, especially her three bogeys.
'I managed to make some birdies when I could but I had a couple rocky holes as well. Just kind of up and down,' she said.
She made a 1-foot birdie putt on 13 to reach 10 under, but gave a stroke back on the 195-yard 16th after sailing her 5-iron tee shot to the right. She hit a strong wedge shot, leaving her with a 4-foot birdie putt on the next hole to get back to 10 under.
The former University of Tulsa standout won the 2005 Franklin American Mortgage Championship for her lone LPGA Tour title.
'I'm making the birdies. I've got to continue doing that,' she said. 'There's too many tough competitors behind me.'
The 18-year-old Pressel began the day on the back nine at 1 under and shot up the leaderboard with four birdies and an eagle in her first six holes to reach 7 under. On the par-5 13th hole, she hit a lob wedge from 54 yards that hopped once and dropped into the cup.
She got her birdie flurry going by sinking putts from 20 and 30 feet.
'For the most part today, I played great,' she said. 'I missed three putts for birdie inside of 10 feet, and I just really had a ton of chances, which was nice for once.'
She cooled off on her back side with three birdies and two bogeys.
'Stupid. Stupid. Stupid,' Pressel said about her three-putt bogey from 20 feet on No. 7.
Pressel and Park are vying to become the youngest winner of a full LPGA Tour event. Pressel got close at last week's season-opening SBS Open. She shared the lead heading into the final day and closed with a 74 to tie for fourth.
Her efforts in the offseason in the gym and on the greens are paying off.
'I worked a lot on everything, just tightening everything up so that I could hit them closer to the hole and make more birdies,' she said. 'I worked a ton on my putting and I think I putted pretty well.'
Julieta Granada (75), who finished second at Turtle Bay, was at 2 over. She fell out of her game after double bogeying her ninth hole, the par-4 18th. Her approach shot fell well short of the green, about a foot behind a wood railing.
Instead of laying up, Granada attempted to pitch over the railing, but whiffed. She angrily threw down her club with the grandstand looking on. She then chipped about 10 feet sideways on to the fairway where she safely hit onto the green and two putted.
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