Harang (2-5) rebounded from a 3 2/3-inning, seven-run effort in his previous outing to dominate the Padres in a 122-pitch shutout, the seventh of his major-league career.
The veteran right-hander issued a pair of walks and struck out eight as the Mariners took the opener of a four-game home-and-home interleague series.
Kendrys Morales went 3-for-5 with a two-run single as Seattle won a second straight after snapping an eight-game skid.
Padres starter Clayton Richard (0-5) was tagged for five runs on seven hits over six full frames.
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