Seattle's Mike Zunino tied the game with a solo home run to right-center field in the eighth.
The Mariners (68-68) kept pace in the American League Wild Card chase with Saturday's win, staying 3 1/2 games back of the Twins for the second spot.
The Mariners relied on the long ball Saturday, as Cano walloped a two-run homer in the third while Segura and Alonso slugged back-to-back homers in the fifth.
Bruce Maxwell and Khris Davis each launched solo home runs, and Matt Joyce joined the party with a three-run shot in the fourth to put A's up 5-2.