The all-time single season performance Mariners rotation

Oakland Athletics v Seattle Mariners
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Mariners 2023 Luis Castillo 

This choice is working under the assumption that Castillo is going to continue his current production through the end of the season. Well, on his way to a top pitching performance in team history, Castillo has made 13 starts for the ‘23 Mariners and has been great so far. 

Currently pitching to the tune of a 2.70 ERA, Castillo is maintaining a 0.991 WHIP, 10.8 SO/9 to 2.0 BB/9, while limiting batters to just 6.9 H/9. 

Even if his production dips slightly, he is well on his way to one of the more impressive pitching seasons in the PNW, with this list serving as the official prediction that he will not only maintain his production, but potentially even slightly improve.