Masterson (7-2) ran his scoreless inning streak to 16 with the 106-pitch performance. The right-hander scattered three hits and walked two while lowering his ERA to 2.83.
Michael Brantley went 2-for-4 with a three-run homer and an RBI single for the first-place Tribe, who reeled off their fourth straight win and their 14th in 17 games overall.
Mariners starter Felix Hernandez (5-3) was touched for six runs (five earned) on eight hits over five frames.
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