Attacking widemen Jese and Deulofeu helped themselves to two goals apiece before Luis Gil got one back for the USA.
Real Madrid prospect Jese headed Spain in front after just five minutes from Deulofeu's cross before the Barca man scored a brilliant second with a curling drive.
Another close range finish from Jese made it 3-0 before half-time and then man-of-the-match Deulofeu made it four after rounding the keeper and scoring from a tight angle 15 minutes into the second-half.
A superb strike from Real Salt Lake forward Gil in the 77th minute did at least put some respectability on the scoreline.
The result gave Spain an ideal start in Group A. In that group's other match France defeated Ghana 3-1 with all the goals coming in the second half.
Geoffrey Kondogbia (Sevilla), Yaya Sanogo (Auxerre) and Jean-Christope Bahebeck (PSG) put France 3-0 up before substitute Yiadom Boakye (Juventus) got a late consolation.
In Group B there were victories for Portugal and South Korea.
The Portuguese defeated Nigeria 3-2 in an entertaining contest in Kayseri with Sporting Lisbon winger Armindo Bangna helping himself to two goals.
However, Nigerian captain Ajagun is sure to attract interest from European clubs after scoring twice himself in a fine overall performance.
The 20-year-old midfielder plays his football with Dolphins in Nigeria but will have impressed the mass of scouts at the tournament and could have scored a hat-trick.
Korea came from behind in their match to defeat Cuba 2-1.
England play their opening match against Iraq on Sunday.
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