Kyle Seager tied it, Chris Herrmann walked it off in wild Mariners extra-inning win

Just get one of these back-loaded bullpens a late-inning lead. That’s been part of the M.O. for both the Oakland Athletics and Seattle Mariners this season.

Well … other than that the A’s clinched a playoff berth and the Mariners will miss out for the 17th consecutive season.

But they entered Tuesday as the only teams in MLB to be undefeated when leading after eight innings, and the Mariners had to deal with a one-run deficit in the ninth against Blake Treinen, who has been discussed among Cy Young consideration as Oakland’s dominant closer.

Of course it would be Kyle Seager – who has been mired in a career-worst season offensively. He tied it with a pinch-hit, RBI single with two outs when he…