Leona Maguire and Stephanie Meadow have made strong starts in the Shoprite LPGA Classic in New Jersey.
After the opening round, Jodi Ewart and So-Yeong Ru sit joint top on six under par after shooting a pair of 65s.
Maguire is only two strokes back on four under par in a tie for 11th spot. The Cavan woman began her opening round with a bogey but registered five birdies thereafter without another blemish.
Two shots further back on two under par is the other Irish player in the field, Stephanie Meadow, the Antrim player beginning with the jolt of a double bogey but finishing strongly with four birdies in his final seven holes to card a 69.
Eight players are tied one stroke behind Shadoff and Ryu at five under 66, including South Koreans Jin Young Ko and Inbee Park, the second- and third-ranked players in the world.
Amy Olson, Canada's Brooke Henderson, France's Celine Boutier, South Africa's Paula Reto, Finland's Matilda Castren and Denmark's Nanna Koerstz Madsen are at five under.