(CNN) -- Stacy Lewis of the United States led the Evian Masters at halfway after finishing with a timely birdie for a second round 69 Friday.
The birdie four at the par-five 18th left her one shot clear of South Korea's Lee Il Hee on 12-under 132.
Fellow American and 2005 winner Paula Creamer and another South Korean, Park Inbee, were three shots adrift on nine under at the joint LPGA and Ladies European Tour event.
But Yani Tseng, No.1 in the Rolex World Rankings, finished on three-over 147 after a second round 71 to miss the cut by a shot.
Lewis shot a course record 63 in the first round and an eagle three on the long seventh left her three under for the day.
But she dropped two shots coming home, canceled out by birdies on the 15th and 18th.
"To be honest, I struggled a little today," she told AFP.
"It is always tough backing up a really good score. In this weather, you have to make birdies. But it is hard not to push too much."
Boosted by four birdies in a row from the 13th, Lee carded a 67 to challenge the leader.
Creamer, yet to drop a shot, carded a 64 while Park's 64 was the lowest of the day.
But they are all chasing Lewis, who has won twice on the LPGA Tour this year and has risen to No.3 in the world.
On the men's European Tour, Denmark's Thornbjorn Olesen led after the third round of the Austrian Open Friday.
Olesen shot a second straight 68 for 16-under 200 at Atzenbrugg, near Vienna. He has led since his blistering opening 64 on the first day.
Rikard Karlberg of Sweden is his nearest challenger on 13 under followed by the quartet of England's Richard Bland, French pair Benjamin Hebert and Thomas Levet, and home hope Bernd Wiesberger.