Hernandez has gone 9-0 in his last 10 starts against the Tigers, becoming the first pitcher to capture nine straight decisions against Detroit since Dennis Lamp reached that total 23 years ago.
Hernandez (2-1) gave up four hits while walking three and striking out two.
Seattle built a 6-1 lead through three innings and cruised to its second straight triumph over the Tigers. Detroit has lost three in a row.
Dustin Ackley singled in two runs during Seattle's three-run second and he had an RBI double in the fifth. Alex Liddi hit a two-run homer in the third.
The loss went to Adam Wilk (0-3), who retired only six batters while giving up six runs on eight hits in two innings.