Webb played a bogey-free round as she began her quest for a fifth straight title at this event. The 27-year-old started on the 10th and picked up a shot with a birdie on the par-three 11th to make the turn at minus-one.
On the front nine at The Royal Pines Golf Club, Webb birdied the par-four fourth and closed out the round with a birdie at the eighth.
'My whole round was a little tentative,' said Webb, who is making her 2002 debut on the Ladies European Tour. 'I didn't hit the ball as well as I would have liked, I think it was due to not playing a tournament round for a few months. All in all, I am happy to get out of it at three-under, so there's no real damage done.'
The 2001 U.S. Women's Open champion was joined by three others in a tie for fifth.
Esterl got off to a scorching start with four straight birdies to open the round. She added another at the par-four sixth to make the turn at five-under.
The 25-year-old climbed to minus-seven after birdies at 10 and 12, but ran into trouble with a bogey at the 14th. She birdied the following hole but closed with a bogey on the last for a round of six-under 66.
'It felt like there was a magnet in the hole,' she said. 'It's a great event here, and a great course and I'll just go out tomorrow and do the same thing, the same routine. It's so close in golf, one day you go out and your putter is hot and shoot six-under, the next day, maybe nothing goes in for you.'
Beck Morgan of Wales posted a five-under 67 to finish alone in second, while Spain's Paula Marti and Michelle Ellis of Australia were knotted at four-under 68.
Annika Sorenstam had only one birdie on the day to go along with three bogeys for a two-over 74.