Luis Castillo pitched six strong innings and Sam Haggerty drove in three runs as Seattle defeated the visiting Oakland Athletics 5-1 Saturday afternoon, just hours after the Mariners clinched their first postseason berth since 2001.

The Mariners (87-70) won their fourth in a row as they attempt to climb the American League wild-card standings to earn home-field advantage in the opening round of the playoffs.

Oakland (56-102) suffered its sixth consecutive defeat.

After allowing a first-inning run, Castillo (8-6), who lost to the A's twice since being acquired from Cincinnati at the trade deadline, retired the final 16 batters he faced. The right-hander allowed one run on two hits, with one walk and eight strikeouts.

Haggerty broke a 1-1 tie with a two-run single in the first inning and added a sacrifice fly in the eighth.

Oakland's Tony Kemp lined the game's first pitch into center field for a single. Sean Murphy drew a walk and, with two outs, Jordan Diaz hit a run-scoring single to left.

The Mariners, who were resting several of their regulars after the late-night heroics and celebration Friday, answered against right-hander Adam Oller (2-8), who was serving as an opener for lefty JP Sears.

Dylan Moore led off the bottom of the first with a double to center. An out later, Carlos Santana grounded a single into center to plate Moore with the tying run. Santana advanced to second on a wild pitch and took third on a passed ball before Luis Torrens and Jarred Kelenic drew back-to-back walks to load the bases. Haggerty lined a two-run single to right, giving Seattle a 3-1 lead.

Sears matched Castillo from the second inning on, as the rookie pitched six scoreless innings while also allowing just two hits. Sears walked two and fanned six.

Lefty Kirby Snead replaced Sears in the eighth and struggled. Jesse Winker and Santana led off with singles and Torrens doubled on a fly ball to right-center that fell between Seth Brown and Chad Pinder. An out later, Haggerty lifted a sacrifice fly to center to complete the scoring.