Mary Hanna has made Australian Olympic history, becoming the nation's oldest competitor at a Games when she rode in the opening round of the dressage competition.
Hanna at 61 years and 253 days, surpassed fellow equestrian Bill Roycroft who competed at the Montreal Games in 1976 aged 61 years and 128 days.
Her appearance in Deodoro on Wednesday also resulted in her joining a select group in volleyballer Natalie Cook and table tennis player Jian Fang Lay as Australia's only five-time female Olympians.
The Melbourne-born rider finished the day in 15th in the individual dressage competition with a personal-best score of 69.643 riding Boogie Woogie 6.
Hanna first represented Australia at the Atlanta Games in 1996 before continuing with Olympic competition at the 2000, 2004 and 2012 Games.
She was thrilled with the performance of her horse.
"He's such a cool little dude in there, he never runs out of energy," Hanna said.
Hanna also rode in the opening day of the dressage team competition along with Sue Hearn, who is 60, became Australia's second-oldest first-time Olympian.
Hearn scored a 65.343 aboard Remmington to give the Australian team an average score of 67.593 to leave them ninth in the competition behind leaders Germany (79.157).
Sailor Harold Brooke, who was 61 when he made his debut at Rome in 1960, remains Australia's oldest first-time Olympian.
The dressage competition continues on Thursday when Lyndal Oatley and cousin Kristy Oatley will be in action for Australian team.