Zara Phillips kept her hopes of Olympic qualification alive with a winning start to the eventing season in Hampshire.
William Fox-Pitt, Mary King, Piggy French and Nicola Wilson are likely to feature for Britain at Greenwich Park in July, leaving one place available.
Phillips, on Silver Lining V, won the open intermediate section D class at Tweseldown Horse Trials near Aldershot.
Lucinda Fredericks took second, while Pippa Funnell finished 20th.
Phillips, who won the gold medal at the 2006 World Equestrian Games, is expected to face competition for the fifth place in the British team from double Olympic bronze medalist Tina Cook, multiple major championship medal winner Funnell and 2009 Badminton and Burghley champion Oliver Townend.
Phillips was in a strong position after the dressage at Tweseldown following a score of 30.
A clear showjumping and cross-country rounds, and just 7.2 in cross-country time faults, saw her take top spot.
Phillips, the Queen's granddaughter, and High Kingdom were 14th in open intermediate section C, a class dominated by Wiltshire-based New Zealander Andrew Nicholson, the World Equestrian Games individual bronze medalist in 2010, who was first and second aboard Avebury and Calico Joe respectively.
Other winners on day one of the trials were Fredericks (Mr Miller 2), New Zealand's Tim Price (Wesko) and George Hilton Jones (Dollar Hill).