GB&Ire unless stated -7 Karen Stupples -5 Ji-Yeon Lee (Kor) -4 Catriona Matthew, Annika Sorenstam (Swe), Natalie Gulbis (US)

The 30-year-old English star carded seven birdies in a bogey-free round.

Korea's Ji-Yeon Lee is in second place after a 67, while Sweden's defending champion and world number one Annika Sorenstam is a shot further back.

Alongside Sorenstam on four under are Scotland's Catriona Matthew and American Natalie Gulbis.

England's Laura Davies, the 1986 champion, posted a three-under 69 to be just four shots off the lead.

Dover-born Stupples, who claimed her first pro win in March this year and finished fourth at last week's lucrative Evian Masters, is now in an excellent position to become the first British winner of this event since Penny Grice-Whittaker in 1991.

But she endured a fraught start to the day, getting caught up in heavy traffic en route to Sunningdale.

"I was only 15-minutes away, but got stuck in traffic and it took 50-minutes," she said.

"By the time I got to Sunningdale, I was feeling very tense and stressed. But, thankfully, as soon as I got on the course everything went very smoothly.

"I only used my driver four times. It was a strategic round that worked really well and I couldn't be happier."

The conditions were great - not a breath of air - and the greens were pure and they were really good for scoring Annika Sorenstam

Sorenstam exchanged two birdies with two bogeys in her outward nine but then recorded four birdies on the inward run as she made the most of the inviting conditions at the Berkshire course.

She said: "It's one of the best starts in the championship for me.

"I wanted to take advantage of my early tee time. The conditions were great - not a breath of air - and the greens were pure and they were really good for scoring."

Playing partner Meg Mallon, who edged Sorenstam into second place at the US Open earlier this month, suffered two double-bogeys in a disappointing round of 75.

Matthew, who tied for third when the championship was last staged at Sunningdale in 2001, claimed five birdies in a promising round.