China's Liu Yu made the most of her early morning start, firing an eight-under par 64 on Friday to join world number one Park Sung-hyun atop the leaderboard of the LPGA Founders Cup.
Liu matched France's Celine Boutier -- a former teammate at Duke University -- for low round of the tournament to seize a share of the halfway lead on 12-under par 132.
South Korea's Park posted her second straight 66 at Wildfire Golf Club in Phoenix, Arizona.
She and Liu were two strokes clear of a group of eight players on 10-under 134 that included overnight leader Boutier as well as former world number one Lydia Ko of New Zealand.
They were joined by Americans Angel Yin and Cheyenne Knight, Sweden's Linnea Strom, That group is headlined by top-15 players Amy Yang of South Korea and Lydia Ko of New Zealand. It also includes Boutier, Americans Angel Yin and Cheyenne Knight, Sweden's Linnea Strom, Denmark's Nanna Koerstz Madsen and South Korean Hur Mi-jung.
Defending champion Park In-bee of South Korea headed a group of five players on 135.
Liu was in the first group off the tee at 10, bouncing back from an opening bogey with three straight birdies.
She followed another bogey at 14 with birdies at 15 and 18, and birdied five holes coming in.
"Just everything kind of clicked all together," said Liu, who admitted that it's not something she would expect to happen every day.
"When a day like this comes, I just am glad I was able to take advantage of it," she said, adding that the chilly temperatures that greeted her group slowed her early.
"My putting definitely helped me a lot on the front nine," she said. "On the back nine the weather warmed up and I was hitting it close and I was able to capitalize on those short- and mid-range birdie putts."
Park also teed off on 10 and after playing her first nine holes in two-under.
She came alive over her final nine, with birdies at five of six holes that included a run of four straight from the first through the fourth.
A bogey at the ninth prevented her from holding the solo 36-hole lead.
"Overall I'm really happy with the play today, especially putting was really good and the shots were better than yesterday," Park said.
Strom was eyeing a share of the lead with nine birdies and no bogeys through 17 holes before a double bogey at 18.
Boutier, who fired eight birdies without a bogey on Thursday, was as low as 13 under after three birdies and an eagle at the par-five 15th. But she fell back with a bogey at 16 and a double bogey at the last.