Fellow American Spencer Smith claimed the overall series title; Mario Deslauriers was top Canadian, 9th with Quatro van de Meerputhoeve.
Belgium and Ireland finished third and fourth at the World Equestrian Center event, with only 7 first-round clears of the 40 starters.
The Olympic champion rode the mare Just Be Gentle to win Thursday's feature event at World Equestrian Center – Ocala.
Canadians grabbed three top-ten spots in the feature event at TerraNova Equestrian Center, which was won by Paul O’Shea and Spy.
The Mexican rider rode his Olympic mount H5 Porthos Maestro WH Z to take the $215,000 class to edge American and Irish competitors.
The Egyptian rider piloted Evergate Stables' mare who is "such a trier" as the WEF winter tournaments head into the home stretch.
Erynn Ballard and Tiffany Foster secured the two qualification spots allocated to Canada, but neither will compete.
The Irish rider's fairly new partnership with the big-strided and sometimes "misunderstood" mare is steadily improving in the five-star ranks.
Ireland's Simon McCarthy and Gotcha grab first place – and their first international grand prix win – under the lights at WEC-Ocala.
Emilie Conter (BEL) wins the Week 9 CSI5* feature, edging Harry Charles (GBR) and Sherlock and Henrik von Eckermann (SWE) with King Edward.