The Americans totaled 88.5108 points for a 2 ½-minute routine that included scissor kicks and spins Sunday night in front of a pro-Russian crowd at Kazan Arena.
The mixed duet is new to the world championships. The event brings men with jelled hair and nose clips into what has traditionally been a female sport dominated in recent years by Russia.
Aleksandr Maltsev and Darina Valitova of the host nation, who led after the preliminaries, settled for silver with 88.2986 points.
Italians Manila Flamini and Giorgio Minisini earned bronze with 86.3640.