American Morgan Pressel and Swede Camilla Lennarth share a one-shot lead after the first round of the Women's British Open.
Pressel, 25, made seven birdies in a round of 66 that gave her the clubhouse lead at St Andrews.
But Lennarth, 25, carded a bogey-free round to match that, with a group of seven just one shot behind them.
Looking to become the first player to win four straight majors, world number one Inbee Park finished on three under.
Britons Catriona Matthew, Liz Young and amateur Georgia Hall are part of a group two shots off the lead.
Defending champion Jinai Shin is one-under-par, while English veteran Laura Davis carded an even par 72.
English youngster Charley Hull, 17, did not manage any birdies in a round of 76, which included three consecutive bogeys from the 15th onwards, that leaves her four-over-par.
Before Lennarth produced a faultless round to draw level, Pressel's only bogey came on the sixth and a stretch of four birdies in five holes on the back nine helped her take the lead.
The youngest-ever winner of a modern LPGA major championship at 18, Pressel told BBC Sport: "It's a neat feeling.
"It's still only the first day and there's a long way to go but it's great to play well on this golf course, which has so much history. I feel like I prepared very well over the previous three days; I had a good gameplan and stayed true to that.
"I hit the ball where I wanted to and I gave myself a few birdie opportunities."
Park finished her opening round on three-under-par, but she had been six under after 10 holes.
She dropped shots at the 13th, 16th and 17th, before a closing birdie on 18.