The Royals, owners of the worst record in the American League and the second-worst mark in the majors, lost their third straight.
Pena's 26th homer of the season came after Sidney Ponson had given up singles to B.J. Upton and Carl Crawford. Ponson (1-7) allowed seven runs on eight hits in 4 1/3 innings.
Tampa Bay took a 4-1 lead into the fifth and broke the game open in that inning with three runs.
Evan Longoria drew a one-out walk and scored on a triple by Ben Zobrist. After Pena was hit by a pitch, Pat Burrell singled home Zobrist and a base hit by Gabe Gross delivered Pena with the third run of the innings.
David Price (4-4) coasted to the victory, giving up a run on five hits in seven innings.
Copyright 2009 by United Press International.