Andrew Nicholson took control at the Rolex Kentucky three-day event after two brilliant clear cross-country rounds put him into first and second.
The world's No1-ranked eventer has dressage scores of 38 penalty points aboard Quimbo and 40.8 on Calico Joe. Teammate Jonelle Richards and The Deputy, in their first Kentucky start, are seventh after an impressive clear cross-country, with just 2.4 time penalties, to sit on 55.1.
Nicholson had plenty of praise for Quimbo, rating the cross-country in their first four-star start together as probably his "most exciting ride ever".
"He is unbelievable," said an elated Nicholson. "For the first time at this level, he is just amazing."
Calico Joe also made the cross-country look easy, but Nicholson said he expected that from one of his more experienced mounts.