Smoak's blast in the first inning handed the Mariners a 3-0 lead and Saunders' fifth-inning clout put Seattle ahead 9-3.
Jesus Montero went 3-for-4 with a pair of run-producing hits and Kyle Seager added a two-run double as the Mariners banged out 14 hits en route to their second straight win over the Royals.
Blake Beavan (4-6) notched the victory despite giving up five runs on seven hits in six full innings. The right-hander didn't issue a walk and fanned three.
Kansas City starter Ryan Verdugo (0-1) lasted only 1 2/3 innings, surrendering six runs on eight hits in his major league debut.
Lorenzo Cain hit a two-run homer while Alex Gordon went 2-for-4 with an RBI triple for the Royals.
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