Pornanong Phatlum and Karine Icher both fired rounds of seven-under 66 on Saturday to share the first-round lead of the Brasil Cup.
The pair owns a one-shot cushion at Itanhanga Golf Club in this two-day, unofficial event.
Katie Futcher is alone in third place at six-under 67, followed by world No. 3 Suzann Pettersen, Brittany Lang and Candie Kung. That trio is tied for fourth at five-under 68.
Paula Creamer, the only other top-10 player in the world in the field this week besides Pettersen, shot a four-under 69 and is knotted in seventh with fellow American Christina Kim.
Phatlum started beautifully on Saturday with three consecutive birdies. She added three more birdies in the last four holes of her opening nine to make the turn at six-under par.
After a bogey at the 11th, Phatlum atoned for the error immediately with a birdie at the par-five 12th. She netted one more birdie, a three at the par- four 16th, to reach seven-under. Phatlum parred out for her share of the first-round lead.
"Today I played really well and I have confidence in my game," said Phatlum, who is winless on the LPGA Tour. "My approach shots and putting were very good today. This course is narrow and we have to concentrate on our target."
Icher, who took third at the Mobile Bay LPGA Classic last week, didn't play the front nine as well as her co-leader on Saturday. Icher recorded only three birdies, but two came at the eighth and ninth.
She continued her fine form around the turn with three birdies and a bogey in her first four holes. Icher birdied the 15th and 16th to join Phatlum in first place.
"My putting was good," said Icher. "It was a good round, a good sensation. I love that course. It's just flat and enjoyable so it was cool. We'll see tomorrow. I'm going to try to do my best, be relaxed."
Defending champion Mariajo Uribe opened with an even-par 73.
NOTES: Tee times were moved up for Sunday with the final threesome going off at 8:39 a.m. (et)...Icher is also winless on the LPGA Tour...2007 LPGA Tour Rookie of the Year Angela Park played her first competitive round in almost 18 months and shot a three-over 76.