The call was overturned, giving Porter a successful challenge.
The decision loomed huge, considering it would have put the winning run on base with sluggers Corey Hart and Kyle Seager due up for the Mariners. Instead, the Astros left the field and prepared to bat.
They won the game on George Springer's walk-off single in the 11th inning, 5-4.
Porter has won four of his five challenges this season, and four in a row.
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.