Kent Farrington won the afternoon event with Austria 2, while fellow American McLain Ward and Catoki took the evening feature.
The US rider has found yet another winning partner, while Canada's Mario Deslauriers and Bardolina nab third place in the rich class.
The first qualifier for Sunday's prestigious Rolex Grand Prix at CHIO Aachen, the Turkish Airlines-Prize, was taken by the US rider.
The pair defended last year's title at the conclusion of the 2022 Old Salem Farm Spring Horse Shows in North Salem, NY.
Friday's win aboard Contagious puts the American at the top of the leaderboard going into Sunday’s World Cup title decider.
It is an exciting Final field of 36 that will vie for top honours at the Exhibition Hall in Leipzig, Germany.
Erynn Ballard (CAN) and Gakhir, her Nations' Cup mount, took fifth place; Tiffany Foster received The Kate Nash Boone Style Award.
The US rider and his Olympic mount edged Belgium's Zoe Conter riding Davidoff de Lassus in the 46-entry field.
Round 4 of this series attracted 65 entries to compete over Anderson Lima's course on the Derby Field, 12 of which came back for the jump-off.
The $75,000 Rosenbaum PLLC Grand Prix saw 32 entries contest a course set by Eric Hasbrouck, with eight advancing to the jump-off.