Ireland's Austin O'Connor and Kate Jarvey's Ringwood Mississippi recorded just four faults in what proved to be a very challenging show jumping phase at the Rolex four star event in Kentucky today.
The round moved the Cork rider up from 19th overnight to a very creditable 13th place in the USA's top three-day event.
Speaking after the competition, 38-year-old former Olympian O'Connor said: "It was a great trip and great experience.
"Ringwood Mississippi proved that he's a real contender for the future.
"I'm delighted with the result and how the horse improved throughout the competition."
The horse's owner Kate Jarvey added: "We're over the moon with the performance, as it was beyond our wildest expectations. Kentucky was very good to us."
Meanwhile Nick Turner, Team Ireland eventing high performance manager, said from Kentucky tonight: "Congratulations to Austin and Ringwood Mississippi's owners Frank and Kate Jarvey .
"It was a very solid performance with huge potential to improve on this great result."
On what was a remarkable day for Irish breeding, nine Irish-bred horses finished in the top 18 places at the renowned event.
Calico Joe finished third for New Zealand's Andrew Nicholson while Ballynoe Castle RM placed fourth for the USA's Buck Davidson.