South Korea's Meena Lee fired a seven-under-par 65 to lead after the first round of the Women's British Open at Carnoustie.
Lee, 29, carded seven birdies in a blemish-free round to finish two shots clear of American Brittany Lincicome.
Scotland's Catriona Matthew, champion in 2009, and Wales' Becky Brewerton were tied for 16th after two-under 70s.
English pair Rachel Jennings and Georgina Simpson are tied for 27th after opening 71s.
Lee's round was made all the more remarkable by the fact she battled through the harshest conditions, playing all 18 holes in torrential rain.
Lee said: "I like links golf. It's very different to what we play on the LPGA Tour and I really enjoyed it today, despite the weather."
A two-time winner on the LPGA Tour, Lee finished three shots clear of a group of four that included the top two Europeans, Germany's Caroline Masson and Swede Sophie Gustafson.
Taiwan's Yani Tseng, the defending champion and world number one, birdied the 18th to stay well in touch on one under par, while world number two Cristie Kerr was a further shot back.
England's Melissa Reid, who has five top-10 finishes on the Ladies European Tour this season and won the Dutch Open in June, carded a three-over 75, while four-time major winner Laura Davies got under way with a 73.