PEORIA, Ariz. -- With an assortment of riches within their starting rotation, the Mariners believe that any one of their five arms would be worthy of making the March 27 Opening Day start -- though they remain mum on the topic as Cactus League play accelerates to full swing.

Yet, barring the unforeseen, the assignment is almost certainly only a two-man consideration -- between Luis Castillo, the veteran workhorse and the roster’s highest-paid player, and Logan Gilbert, the homegrown ace and rotation’s lone All-Star last season.

“Hard to say at this point, but we're getting there,” Mariners manager Dan Wilson said Monday morning. “I think we're starting to put the pieces together here. I don't know if there's a date that I can give you guys, but we're definitely kicking it around.”

That this is a topic of speculation is mostly due to how Seattle rolled out its rotation once Cactus games began, with Gilbert taking the mound first in Monday’s 12-8 win over the Brewers and Castillo to follow on Tuesday against the Dodgers. George Kirby will slot third, on Wednesday vs. the A’s. Seattle hasn’t formally announced its probables after, but presumably it’d be Bryce Miller then Bryan Woo.

The club held off on deploying any of its starting five over the weekend to ease them into action, instead turning to Jhonathan Díaz, Logan Evans and Emerson Hancock, in order.

There’s still over a month until the regular-season opener against the A’s at T-Mobile Park and three off-days this spring, plus two more after they leave Arizona, to re-slot their starters. But going with Gilbert first could offer a hint to the direction that the Mariners are leaning.

“It'd be awesome if it happened,” Gilbert said, “but I mean, we have five Opening Day starters, so I don't think anybody should get their feelings hurt, because on different teams, we would probably all start the first day. So it's a huge honor to whoever gets it.

“Obviously, Castillo, being the veteran, is very, very deserving. But every time I'm out there in spring I feel like I’ve got to prove myself all over again. So I don't want to get ahead of myself.”

How Gilbert is handling the situation speaks to his maturity on and off the mound. He’s firmly found his voice within the Mariners’ clubhouse as measured and thoughtful -- much like the demeanor he has when attacking hitters on start days.

The towering righty has blossomed into one of the most consistent right-handers in the American League, leading the Majors last season in innings (208 2/3) and WHIP (0.89) while compiling a 3.23 ERA (113 ERA+, where league average is 100) to go with 220 strikeouts and 37 walks. He also held hitters to a .589 OPS, fourth-best in MLB.

And he’s continuing to reach for new heights.

“He's really become a leader amongst that pitching staff, and what he continues to do is get better,” Wilson said. “He continues to work at it, and there is no quit in him.”

Castillo’s credentials are also in play, as is how he’d absorb a decision for anyone else to start on Opening Day -- even if it’s unsaid publicly by both himself and Mariners management. Castillo wasn’t as dominant in 2024 as he was from 2022-23, with a 3.64 ERA (101 ERA+) while seeing his season cut short by three weeks due to a Grade 2 right hamstring strain. “La Piedra” started each opener since coming over in a 2022 Trade Deadline blockbuster.

There’s also the component that the Mariners fielded trade interest on Castillo this winter yet preserved their relationship with him by keeping his agent appraised.

“I'm 100 percent happy,” Castillo said through an interpreter. “I mean, the talent we have this rotation, it's my third year here, and once you're here this long, you’ve kind of built a family here. So I'm happy that I'm here to see the talent and just getting ready to go.”

Castillo has said each spring that he carries three explicit goals entering each season -- to start on Opening Day, make the All-Star team and win the AL Cy Young Award -- which he reiterated last week.

“Those are the three goals that I’ve had throughout my whole career and those are the three goals I’m coming in with now,” Castillo said. “And I’m going to continue having those goals until the day I retire.”

It’s clear that the Mariners recognize the decision they face -- and it appears to be a good problem to have.