The United States, winners in 1991 and 1999, became the first nation to win the crown three times and avenged their loss to Japan on penalties in the 2011 final.
Lloyd, 32, scored her first goal after just three minutes on the pitch at Vancouver's BC Place Stadium with the second coming two minutes later, and her third after 16 minutes.
Lauren Holiday (14) and Tobin Heath (54) also found the net for the Stars and Stripes.
Yuki Ogimi got one back on 27 minutes for the Asian champions with their second coming thanks to a 52nd-minute own-goal by US defender Julie Johnson.
It was the third meeting between the two teams in a major championship with the Americans winning the Olympic gold ahead of Japan in 2012, when Lloyd scored both goals in a 2-1 win.
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