Shin, playing late in the day in round one, recorded a round of 66 to lead by one over the brilliant Canadian teenager Brooke Henderson with Webb tied with Moriya Jutanugarn and Charley Hull in 3rd position.
Shin is a former US Junior Champion and is in her fifth season on the LPGA Tour although without a win to this stage. Her round was highlighted by an eagle at her 15th hole.
For Webb it continues some better results in recent weeks and further highlights he capacity to perform well in the big events.
"I hit the ball really solid today," said Webb. "I missed a couple of fairways I think. My iron play was really solid and made a few putts. But I didn't really have to work too hard on a lot of par putts today, so I think that's always nice out here that you don't have that stress.
"But yeah, it was a really solid round and I got off to a good start, with birdies on 10 and 12. So I think that really settled me down to really trust what I've been doing, and I did it from start to finish today. So I was really happy about that."
"I hope so," said Webb when asked if she still had thoughts of winning another major. "That's why I'm still out here. If I didn't think that I could, I wouldn't even be trying. But I definitely think my game is as good as it's ever been. It's just a matter of getting out of my own way and allowing that to happen. I did that for the most part today, which that's probably what I'm most proud of."
Minjee Lee was the next best of the Australians when she finished with a round of 72 to be in 40th position.
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