The $235,000 Friday feature at Thunderbird Show Park also marked the American's first 5* victory here; top Canadian was Ali Ramsay, 4th.
The Irish rider rode Theo 160 to the win in a field of 52 ; Canada's Mario Deslauriers has two in the top 10.
Thunderbird Show Park's Odlum Brown BC Open starts June 1st and also features the $235,000 Longines Grand Prix.
Thunderbird Show Park was the site of the $200,000 team competition, won by Eugenio Garza Perez, Ashlee Bond and Bliss Heers.
The Irish rider rode Brooklyn Heights, a relatively new mount; plus an update on Dieu Merci, who was pulled up during the class.
The Irish rider rode Nadal Hero & DB to the stallion's second 5* win of the week; Canadian Anya Bereznicki dominates U25 division.
The Irishman aboard Ariso bested a 10-horse jumpoff; Vanessa Mannix and Kingston are the top Canadians in 8th place.
Show jumping competition got underway at Wesley Clover Parks with the win coming aboard Dublin, owned by Millar Brooke Farm.
The same four Canadian horse-and-rider combinations as La Baule finished in fifth place among the 10 countries competing.
Belgium had to settle for second, with the Netherlands in third after an exciting afternoon of competition in Piazza di Siena.