New Zealander Andrew Nicholson is firmly on course for another title just a week after winning the Land Rover Burghley Horse Trials.
Nicholson, a member of New Zealand's bronze medal-winning eventing team at London 2012, leads the Blenheim CIC three-star class in Oxfordshire.
A clear round in Saturday's showjumping phase means that Nicholson will take his dressage score of 35.1 penalties on Quimbo into Sunday's cross-country finale.
Britain's Piggy French remains second with West Side despite collecting three showjumping time faults, with German Bettina Hoy third aboard Designer 10.
British number one William Fox-Pitt, meanwhile, holds fourth spot with Bay My Hero.
The CCI three-star section continues with cross-country, when Australian Olympic rider Christopher Burton will look to retain his overnight lead on Underdiscussion.
Fox-Pitt showed his class in the CCI three-star competition, delivering a brilliant clear cross-country round inside the time on Seacookie.
He was one of just six riders from 88 starters to achieve that feat, and it takes him into the showjumping finale on Sunday on a score of 39 penalties as leader.
New Zealand's double Olympic champion Mark Todd lies second with Conair on 42 penalties, just ahead of Fox-Pitt's London 2012 Great Britain colleague Tina Cook and De Novo News, with Oliver Townend and Outside Chance fourth.
Burton dropped out of contention after a disappointing cross-country round saw him pick up 20 jumping faults and eight time penalties.