For most of Game 1 on Tuesday, the Seattle Mariners looked poised for an upset in their ALDS matchup with the top-seeded Houston Astros.

Yordan Alvarez had other ideas. With his Astros facing a 7-5 deficit in the bottom of the ninth inning, the Houston slugger launched an 0-1 pitch from Robbie Ray into the right-field stands for a 3-run walk-off home run to secure an 8-7 win.

The upper-deck blast concluded a rally from 4-0 and 7-3 Houston deficits to secure a 1-0 series lead for the Astros.

Controversial pitching change preceded Alvarez's heroics

Mariners manager Scott Servais pulled closer Pat Sewald with two outs in favor of Ray in an apparent effort to set up a lefty on lefty matchup with Alvarez. Sewald had allowed two runners on base in the inning, hitting David Hensley with a pitch, then allowing a Jeremy Peña single up the middle to put runners on first and second.