Masterson (12-7) outdueled Rangers starter Yu Darvish, scattering five hits over 7 1/3 innings. The right-hander walked one and struck out eight in the 113-pitch gem.
Michael Bourn provided the game's only run with a first-inning homer.
Darvish (9-5) was hung with the loss despite yielding only the one run on three hits in six innings. He walked four and struck out 11.
With the loss, second-place Texas fell five games behind AL West-leading Oakland.
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