Buck batted 3-for-4 with a homer and Alberto Callaspo added two RBI for the Royals, who produced a game-winning three-run rally in the eighth inning.
Reliever Juan Cruz (1-0) got the win with a perfect eighth inning and Joakim Sona struck out the side in the ninth for his third save.
Phil Coke (0-1) gave up two runs in the eighth and took the loss.
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