Kerr, also the LPGA State Farm Classic champion this year, birdied three of the last four holes in her bogey-free round on the links-style Senator course at the Robert Trent Jones Golf Trail's Capitol Hill complex.
"It's fun to be at the top of the leaderboard," Kerr said. "But it's only Thursday. You can't win it on the first day, but you can lose it, so it's great to be in this position."
The third-ranked Kerr topped the leaderboard a day after missing the pro-am because of illness.
"I didn't feel that great in the morning," Kerr said. "For like a week and a half I've been sick. I was starting to feel better on Tuesday. I worked out and got a massage and I just overdid it. I woke up and just couldn't get out of bed. I just rested most of the day and came out here and played great today."
Long-hitting Brittany Lincicome was two strokes back at 67 along with Christina Kim, Vicky Hurst, Giulia Sergas. Silvia Cavalleri was 5-under with a hole left when play was suspended because of darkness.
Top-ranked Ai Miyazato, also feeling under the weather, opened with a 70.
"I'm pretty satisfied about today because I've been sick since last week," Miyazato said. "I stayed calm and just let it happen. So it was all right."
U.S. Women's Open champion Paula Creamer had a 71 in the tour's first event since the Northwest Arkansas Championship ended Sept. 12.
Last year, Lorena Ochoa successfully defended her title for the last of her 27 LPGA Tour victories. The Mexican star retired in May after making five winless starts this season.
Kerr has held the top spot in the world four times this year, the last in mid-August.
"It's definitely driving me," Kerr said. "I'm just going to keep doing what I'm doing. Obviously, that's the goal. To end up being No. 1 at the end of the year, one would think that I would have to win at least one more tournament."