The American triumphed after a six-rider jump-off on board 12-year-old Holsteiner gelding Caillou.

It is the first World Cup win of the season for Cook, who went double clear and clocked the quickest jump-off time of 36.75sec after entering the arena last.

"It's always fun going last," he said after his win at Murieta Equestrian Center.

"You know what you have to do. 

"It gives you a better feeling when you ride, because you know that whatever you do, you stay there."

Five of the six jump-off riders went clear for the second time.

Ireland's Conor Swail, riding Koss van Heiste, took silver as his time of 37.35 was surpassed at the death by Cook.

Guy Thomas of New Zealand, on board Jonkheer Z, claimed bronze with a time of 38.95.

"Conor went inside [to the last fence] and did [one less stride], which I very well could have done," Cook said.

"But I saw how the turn after was, so I said I'd go around and do [one extra stride] and turn after quicker."

Cook has cemented himself at the top of the North American League's west coast standings with 37 points.

Compatriot Zazou Hoffman sits second on 19 with Kelli Cruciotti completing an all-American top three on 17.

Riders around the world are trying to qualify for the World Cup Final in Las Vegas in April.

The North American League continues in Columbus in Ohio tomorrow.