Beltre, who hit a two-run homer in the seventh, drilled a single up the middle with the bases loaded and brought Craig Gentry in with the game-winner.
The victory extended the Rangers' lead in the American League West to five games over the A's.
Mitch Moreland and Josh Hamilton also drove in a run apiece for the Rangers.
Tyson Ross (2-11) took the loss in relief for Oakland. Josh Donaldson drove in two runs with a home run in the second inning.
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