Women's British Open champion Ariya Jutanugarn shot a six-under 65 to claim the first-round lead in the Rio 2016 tournament.
Jutanugarn, 20, won her first major at Woburn last month, the Thai taking the title from Park Inbee, who missed out in order to recover from a thumb problem ahead of golf's return to the Games.
That decision appears to have paid dividends for the South Korean, who sits just one shot back after a bogey-free round on Wednesday, suggesting she has put her injury woes behind her.
Indeed, Park - who completed a career grand slam last year - was the clubhouse leader, but saw her advantage wiped out as world number two Jutanugarn earned gains at the 14th and 16th to surge to the summit.
Park's compatriot Kim Sei-young is also on five under, with Nicole Broch Larsen (Denmark), Candie Kung (Chinese Taipei) and Carlota Ciganda (Spain) a further stroke adrift.
New Zealander and world number one Lydia Ko recovered from going two over across the first four holes to sign for a 69.