Charlotte Fry admitted her Olympic Games debut "could not have gone much better" as she cruised into the individual dressage final at Tokyo's Equestrian Park.
The 25-year-old, whose late mother Laura rode for Britain in the 1992 Barcelona Olympics, topped her qualifying group with Everdale on a personal best grand prix score of 77.096 per cent.
Two riders from each of six groups – plus the next six-best finishers – will contest Wednesday's individual final.
And Fry's outstanding performance under the floodlights also meant a strong start to British team hopes, with Charlotte Dujardin and Carl Hester completing a powerful trio.
Hester, who at 54 is Team GB's oldest competitor in Tokyo, showcased all his experience with a solid display as heavy rain fell.
Gloucestershire-based Hester, riding in his sixth Olympics, finished fourth in Group C aboard En Vogue on 75.124 per cent.
He will now have to wait until the end of Sunday's action to discover whether he has done enough to join Fry in the individual final.
Double Olympic champion Dujardin begins her individual and team quest among Sunday's late starters that also include Germany's multiple gold medallist Isabell Werth.
And while Germany remain clear favourites for team gold, Britain made an impressive start as Fry built the foundations in nerveless fashion.
"I was really happy with it," she said. "It couldn't have gone much better, to be honest.
"He (Everdale) definitely knew it was a big occasion. He was so concentrated today. It was such a great feeling.
"We have really kind of grown up together and built a really good partnership. I enjoyed every second of it, and he felt like he was enjoying it as well.
"You never know how it is going to feel when you go into the arena, and every arena is different, but I really trust him and he really trusts me, so that kind of situation we don't worry about too much."
