HOUSTON -- Much has justifiably been made about the Mariners’ struggles against the Astros and even more so at Minute Maid Park. But Seattle's roster looks different from the last time the team was here in late July when it wrapped the season series against the American League West champs.

It includes a massive addition, one that helped catapult the Mariners from Wild Card hopefuls down the stretch to firmly belonging in the AL Division Series -- in large part due to his efforts.

“We have not played the Astros with Luis Castillo on our roster,” Mariners manager Scott Servais said on Tuesday ahead of Game 1. “He will not play in today's game, but I hope he factors very, very big in this series.”

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As expected, Castillo was named Seattle’s Game 2 starter in this best-of-five round, and he’ll pitch on six days’ rest following his brilliant performance in the Wild Card Series last Friday when he blanked Toronto over 7 1/3 innings. He’ll work opposite All-Star Framber Valdez, the lefty spin specialist who emerged as an AL Cy Young Award candidate in the second half.

Houston announced Lance McCullers Jr. will start Saturday's Game 3, but the Mariners will hold off on slotting the rest of their rotation based on how the first two games play out. It’s possible George Kirby gets that assignment, but that’d likely necessitate him not pitching in Games 1 or 2 to ensure he’s rested enough.

“We're going to play it by ear, see where we're at,” Servais said. “I think that's the best way to go right now for us.”

Castillo has never pitched at Minute Maid Park, which can be one of the most hostile road environments and among the most hitter-friendly in the Majors due to its quirky dimensions. He’s made one start against the Astros over his six-year career, throwing six innings and scattering just two hits while striking out seven in a win for the Reds on June 17, 2019.

Some Seattle starters, most notably Robbie Ray, have struggled mightily in this ballpark, but Castillo could be a curious case because he thrives in big moments.

“I've kind of talked to them about the park, but like I'm not really focused on the dimensions of the park,” Castillo said through interpreter Freddy Llanos. “When I go out there, I'm focused on what kind of pitches that I'm going to throw.”

Castillo’s commentary illustrates how simplistic he is on the mound -- because he can be. His stuff has been good enough that he can throw either rendition of his fastball, both touching 100 mph, and have the conviction that it’ll miss bats. As such, only so much scouting and analytics can go into the preparation for an ace with that kind of arsenal.

“I prepare every time I go on the mound to throw as fast as I can. Batters are also trying to prepare to see what kind of pitch is coming for them,” Castillo said. “But, yeah, there's always a counter to what you do, and batters can get a hit on it.”

The stuff, confidence and execution have drawn the eyes of baseball fans well beyond the Pacific Northwest in his short stint in Seattle of just 12 starts. But it’s how Castillo has thrived in such big moments that has also stood out.

There was his Mariners debut in front of a ticketed 42,169 in New York against a Yankees team that aggressively pushed to acquire him at the Deadline, then against those same Yankees with eight shutout innings to outduel All-Star Gerrit Cole in his T-Mobile Park debut in a game that will go down as one of MLB’s best in 2022. Then there was the overpowering outing in Toronto.

The “Big Game Pitcher” label might be cliché, but it has applied so far. 

“There'll be challenges, no doubt,” Servais said. “But I think just the confidence that he brings to our team every time he steps on the mound, it's as high as it's gonna get and it should be. He's one of the best pitchers in the league.”