Piggy French underlined her Olympic selection credentials with a commanding performance at the Subaru Houghton International Horse Trials in Norfolk.
Leicestershire-based French, who was Badminton runner-up and Olympic Test event winner last year, took victory in one of two CIC 3-star sections.
She won section C on Jakata, and was well placed aboard DHI Topper in section D, but a run-out late on the cross-country course cost her dear and she slipped to 19th spot.
"Jakata went really well without a big effort," French said. "He was on his game and in a different league."
After recent cancellations due to heavy rain of key pre-Olympic events Badminton and Chatsworth, London eventing hopefuls were out in force in glorious conditions at Houghton.
British performance manager Yogi Breisner looked on as French guided Jakata to victory over 2011 Badminton champion Mark Todd, while Belton Horse Trials winner Sarah Cohen was third with Treason and Mary King 11th on Imperial Cavalier.
French, King, world number one William Fox-Pitt and Nicola Wilson are expected to fill four places in Britain's five-strong Olympic team, which is due to be announced after next month's Bramham International in Yorkshire.
It was not such a good day for Fox-Pitt, though, after he fell from Neuf des Coeurs at obstacle 22 of cross-country in section D. Both horse and rider were fine.
Australian Sam Griffiths, riding Real Dancer, won the class, with Britain's Charlotte Agnew second and German challenger Andreas Ostholt third.
King, who is on course for her sixth successive Olympics, said: "It always gets more nerve-wracking the closer we get to an Olympic competition.
"The cross-country course at Houghton was wonderful. There were lots of accuracy questions and it was very educational for young horses.
"The ground has dried up a lot through the week, and we are so lucky to be here. It is perfect timing."