Mariners promote notable prospect to help short-handed staff vs. Astros

The Seattle Mariners are once again dipping into their well-stocked farm system, calling up right-hander Blas Castano ahead of a critical stretch against the division-rival Houston Astros. The move comes as the club scrambles to cover innings after a short outing from George Kirby, who made his long-awaited season debut Thursday night.

Kirby, returning from right shoulder inflammation, lasted just 3.2 innings at hitter-friendly Daikin Park, surrendering five earned runs on 72 pitches. While his return is an encouraging development in the long-term, his brief outing further stressed an already overextended bullpen. Seattle relievers were forced to eat 4.1 innings, setting the stage for yet another roster move.

Pitching prospect Blas Castano joins Mariners for MLB debut

Castano is a 26-year-old righty whose promotion marks his first call-up to the big leagues. Though not a top-tier prospect in some industry rankings, Castano has quietly carved out a niche as one of the more consistent arms in Triple-A Tacoma. Through 10 games (seven starts), he owns a 2–1 record with a 3.43 ERA, a 1.25 WHIP, and 28 strikeouts across 44.2 innings pitched. His profile isn’t flashy, but his stuff is effective.

What makes Castano intriguing is a five-pitch mix built around deception and inducing ground-balls rather than overpowering hitters with velocity. His sinker, averaging 93.1 mph, is his bread and butter — a pitch designed to induce weak contact. It’s complemented by an 82–83 mph slider, an 87–88 mph changeup that some scouts consider his best secondary offering, and an 89 mph cutter used to keep left-handed hitters off balance. He’ll also mix in a four-seam fastball on occasion, though it’s more a variation than a primary weapon.

The Mariners aren’t expecting Castano to strike out the side — that’s never been his game. But what they do need is a pitcher who can keep the ball on the ground and eat innings if called upon, whether as an opener, long reliever, or emergency starter. His command and pitch sequencing have earned him trust at every level of the minors, and now the club will see if it can translate to the majors.

With a tough Astros lineup looming and the bullpen running on fumes, Blas Castano's debut could be coming at an opportune time — both for him and for the Mariners.