Mariners' Opening Day rotation shows how far Seattle's come entering 2026

Luis Castillo was the Seattle Mariners' Game 1 starter in the playoffs in 2022, and their Opening Day starter in 2023 and 2024. That's a nice run for any ace, but it officially ended when Logan Gilbert took over Opening Day duties last year. And now, that run is just plain history.

After an Opening Day roster drop on Wednesday that was light on surprises but heavy on news, the Mariners subsequently revealed how their rotation will line up to begin the 2026 season. The surprise is that Castillo is not the No. 2, No. 3 or even No. 4 starter. He's last in line at No. 5.

There's likely what they used to call "strategery" at play here. Emerson Hancock is only in the rotation because Bryce Miller is on the injured list with an oblique strain, and that only figures to keep him out for a couple of weeks. Once Miller returns, the Mariners can plug him into Hancock's No. 4 spot without having to rearrange anything.

Even so, "Luis Castillo, No. 5 starter" is not something Mariners fans had on their bingo cards last year. Or even as recently as a couple days ago, for that matter.

Mariners make Luis Castillo the most overqualified No. 5 starter in all of MLB

Castillo is a three-time All-Star who was a top-five finisher in the AL Cy Young Award voting just three years ago. And even as his stuff has diminished across the last two seasons, he's still pitched to a 104 ERA+ across 356 innings.

The 33-year-old had a disastrous spring, pitching to a 7.80 ERA over five starts, but he managed to bring it home in a strong way. In his last two outings in Peoria, he allowed three earned runs over 9.0 innings.

So why, apart from the potential strategery, is he the Mariners' No. 5 starter? Well, who are you putting him above in this rotation?

Logan Gilbert, Bryan Woo and George Kirby have each notched an All-Star nod and a top-10 finish in the AL Cy Young Award voting within the last three years. Each is also in the thick of his prime, whereas Castillo's is in the rearview.

As he led the Mariners in rWAR in 2024, Miller would have been a fair choice over Castillo if he'd been healthy. It's harder to extend that same courtesy to Hancock, given his career 4.81 ERA in the majors. But he was impressive in spring training, racking up 21 strikeouts against one walk with whiff rates north of 50 percent on his four-seamer and sweeper.

Notably, The Athletic ranked the Mariners' rotation as the No. 2 unit in the league under the assumption that Castillo would be their third starter. But him in the No. 5 spot doesn't really change anything. Health permitting, matching or even exceeding the rotation's MLB-best 3.38 ERA from 2024 is still the goal.

Just as it was then, being the ace is no longer Castillo's part to play in 2026. He just needs to provide above-average innings, which is typically something teams can only wish for with a No. 5 starter.