Hernandez (2-0) retired the first 11 batters on the way to his 16th career win over the Athletics, his most against any team. Hernandez walked one and struck out eight while allowing a run on six hits over 8 1/3 innings.
Fernando Rodney got the final two outs to record his first save with the Mariners. Robinson Cano had two hits.
Dan Straily (0-1) allowed three runs on six hits over his six innings. He walked one and struck out seven.
Straily carried a shutout into the fifth inning before Ackley's towering two-run shot gave the Mariners a 2-0 lead.
The Mariners are now 4-1 to start the season. They close their series with Oakland on Sunday at 1pm.