It's the A's 17th division title and first since 2013.
At 33-20, Oakland currently owns the third-best record of the three division leaders. The Athletics would host the Astros in a best-of-three first-round series at the Coliseum if the postseason started today.
Houston's loss officially ends its three-year reign atop the AL West. The Astros now hold a 3 1/2-game lead on Seattle for second place in the division.