Britain's William Fox-Pitt made an impressive start to day two at Kentucky as he continues his bid for eventing's Grand Slam.
The current Burghley champion, riding Parkland Hawk, went clear of overnight leaders Brent Martin and Remington XXV.
Their 41.3 dressage score left them second midway through the day's action behind Allison Springer and Arthur.
The £220,000 Grand Slam prize is awarded for consecutive wins at Kentucky, Badminton and Burghley.
Fox-Pitt, who has won medals at the last two Olympics, said he wanted the event to benefit his horse: "I just want to show that he can consolidate his form from Burghley.
"I would just like him to have a very good experience here, and do as well as he can.
"The most important thing is that he goes well and comes out of it well.
"He is one of my horses possibly lined up for the Olympic Games in the summer, so I just want him to have a good experience and get some more miles, and what better place to do it."
The capture of three-day eventing's trio of four-star events can be completed in any order so long as the rider holds all three at once, a feat only one rider has previously accomplished - Fox-Pitt's Team GB colleague Pippa Funnell, nine years ago.
This year's Badminton Horse Trials take place from 3-7 May. The London Olympic competition, being held at Greenwich Park, begins with team dressage on 1 August.