First-round leader Mi Hyun Kim was two shots off the lead at 8-under-par 136 while fellow Korean Grace Park was one shot further back at 7-under-par 137.
Icher, playing in front of a home crowd at Evian Masters Golf Club, was two strokes behind Kim to start the round. She began to chip away at the margin with a chip-in birdie at the third and added another at the fourth to reach 6-under.
She birdied the par-5 seventh and hit a sand-wedge within three feet of the hole at the ninth to move to 8-under and tie Kim, who had birdied the first and the fifth.
At the 11th, Icher drained a 40-footer for birdie to climb to 9-under but was soon matched by Kim, who made a birdie of her own at the same hole.
Icher took the outright lead with a seven-foot birdie at the 16th and parred the two remaining holes to stand atop the leaderboard midway through the tournament.
'I do not have the fate of the world,' said Icher. 'Second year on tour, so I learn.'
The 23-year-old Frenchwoman finished first at the 2000 Ladies European Tour Qualifying School. She went on to win twice during her rookie campaign in 2001 and earned her first victory of 2002 at the Caja Duero Open de Espana in May.
Sorenstam was lurking just one behind Icher after a round of 5-under 67. The Swede collected three birdies on the front nine and knocked a 4-wood one foot from the hole for birdie at the 15th. She had a chance to tie Icher for the lead at the par-5 last, but her eagle try missed as she settled for birdie.
'I gave myself a lot of opportunities, like that eagle putt on 18,' said Sorenstam, who won this event in 2000. 'I had a lot of chances out there, but the greens are still not something I'm used to. It's been tough to make the transition from last week. But if I keep hitting them close enough, they'll drop eventually.'
Pak, who captured her second LPGA Championship last week, matched the course record with a round of 8-under 64. Pak had a share of the lead after a birdie at the 16th but a three-putt bogey at the very next hole dropped her out of the top spot.
The 24-year-old, who became the youngest woman to win four majors with her victory last week, closed with a birdie at the last to join Sorenstam in a tie for second.
'It was fun today,' said Pak. 'Mentally, everything is set.'
Lindley put together a remarkable stretch to close out her round. The 30-year-old landed her tee shot inside three feet of the cup at the par-3 14th for the first of five consecutive birdies en route to a round of 6-under 66.
Cristie Kerr posted a round of 68 to finish alone in seventh at 6-under-par 138. She was followed by Wendy Doolan, Catriona Matthew, Maria Hjorth, Vicki Goetze-Ackerman, Carin Koch and Mhairi McKay, who were all tied at 5-under-par 139.
Suzann Pettersen and Jackie Gallagher-Smith are tied for 14th at 4- under-par 140.
Defending champion Rachel Teske recovered from an opening-round 74 with a 2-under 70 Thursday. Teske finished 10 shots off the lead at even-par 144.
Full field scores from the Evian Masters