Alex Gordon hit a two-run homer, Billy Butler went 5-for-5 with an RBI and a run scored, and Emilio Bonifacio went 4-for-6 with two runs scored for the Royals, who took three of the four games in the series.
Kansas City starter Jeremy Guthrie went six innings, giving up five runs on seven hits.
Louis Coleman (3-0) got the win in relief.
Seattle starter Joe Saunders went 4 2/3 innings, allowing three runs on 11 hits.
Ruffin (0-1) took the loss.
Duggar sisters unveil Christian dating rules in new book
Astronomers offer more expansive view of universe