Captain Steve gave America its third victory in the six runnings of the world's richest race at Nad Al Sheba.
The Bob Baffert-trained Captain Steve (7-4) was sent to the front by Jerry Bailey inside the final furlong of the Dubai World Cup and the combination strode clear to beat the front-running Japanese horse To The Victory by three lengths.
Hightori finishing strongly to claim third half a length away.
America had previously won the £4million contest with Cigar (1996) and Silver Charm (1998) and Bailey, who rode the first-named, also partnered Singspiel to victory in 1997.
After the victory Bailey admitted to be being worried by To The Victory's commanding advantage turning for home.
He said: "I was concerned off the home turn because the leader looked to be travelling and my fellow was a bit flat. That's why I pulled the trigger a bit earlier than I wanted to. In the end I went too soon."
The other joint-favourite Godolphin's Best Of The Bests finished a disappointing eighth under Frankie Dettori.