Morse drove in four runs for the Mariners and Kyle Seager tallied three hits.
Hisashi Iwakuma (1-0) benefited from the Mariners' nine-hit attack. Iwakuma notched the win on one run off two hits in six innings. He struck out seven before stepping aside while the bullpen shut the Athletics out in the final three innings.
Jarrod Parker (0-1) lasted five innings and took the loss. Parker was charged with four runs on five hits and three walks.
Yoenis Cespedes hit a solo home run in the second inning to provide the Athletics' second run in as many games this season.