#2 Seattle Mariners
The Astros toughest opponent en route to a World Series may very well have been their ALDS opponent, the Seattle Mariners. The upstart Mariners may have been swept, but they led or were tied almost the entirety of the series. It took a historic Yordan walk-off in Game 1 to overcome a 7-3 deficit.
Seattle led into the sixth in Game 2 before Yordan again put the Astros ahead on a two-run shot. And who can forget the 18-inning marathon in which Seattle kept Houston's vaunted lineup scoreless through 17 lineups.
These guys were good, and this year they are even better. Julio Rodríguez is still at the top of the lineup, and he's got more than just Ty France and Cal Raleigh behind him. The Mariners addressed their biggest area of need when they acquired Teoscar Hernández to play a corner outfield spot, traded for Kolten Wong to play second base and signed AJ Pollock.
They have three rotation pieces that should be very, very good in Luis Castillo, Logan Gilbert and George Kirby. Robbie Ray is a bit of a question mark depending on who shows up, and Marco Gonzales is there to eat innings, but their front office has been aggressive the last couple of seasons, and it wouldn't be a surprise if they land another starter headed into October.
Their bullpen is full of flamethrowers, especially Andrés Muñoz. Seattle is entirely capable of seeing their AL West foe in the ALCS. Only one team is more likely to reach the ALCS, and it's the team Seattle knocked off in the Wild Card round.