Clarke Johnstone and Orient Express. © Jan Sutherland
Johnstone, 24, who is based in Britain, is the first to Kiwi to win the prestigious series. Just one of the 34 combinations to make it through to the showjumping went clear, with Johnstone and Orient Express taking three rails and Mark Todd and NZB Campino two, to finish eighth.
Johnstone went into the showjumping knowing a clear round would give him a win in the final, but he says it wasn't Blue's (Orient Express) day.
"It was a very difficult track," he said. "The ground was very hard, it was hot and he just didn't jump well."
Johnstone, who was part of the bronze medal-winning team at the World Champs in Kentucky last year, ranks this as his most important win.
Going into the event he didn't think he could be beaten, but it was never a given until prize giving, where he was also presented a trophy as the youngest competitor.