Laura Collett delivered another outstanding dressage display that lit up the Equi-Trek Bramham International Horse Trials in Yorkshire.
Wiltshire-based Collett swept past overnight CIC three-star leader Lucy Jackson by posting a score of 37.5 penalties on Rayef.
Collett and Rayef led Badminton after the opening day last year, ending with an eighth-placed finish that confirmed them as genuine challengers for Olympic selection.
Although Rayef's cross-country performances have not matched that dressage excellence on a consistent basis, Collett knows a good result at Bramham should keep her in the selectors' thoughts.
The five-strong British team for London is due to be announced next week.
William Fox-Pitt, Mary King, Piggy French and Nicola Wilson are expected to claim four of those places, but the fifth is presumed to be wide open with riders like Collett, Tina Cook, Sarah Cohen, Lucy Wiegersma and Zara Phillips all in contention.
After the cancellation of key pre-Olympic events Badminton and Chatsworth last month due to wet weather, Bramham has taken on added significance in terms of Olympic selection.
Collett, meanwhile, held an advantage of 3.6 penalties over Jackson and Animator II, with Belgium's Karin Donckers third, and Fox-Pitt (Avoca Alibi) retained his lead in the CCI three-star class.
Dressage in both sections concludes on Friday, with cross-country and showjumping scheduled over the weekend.