Mariners say goodbye to longtime leader Castillo, set to welcome Domínguez

SEATTLE -- The Mariners’ bullpen will get a boost via new acquisition Seranthony Domínguez on Tuesday, as the veteran is expected to arrive at T-Mobile Park for their upcoming series against the Tigers.

But first, the clubhouse said goodbye to Luis Castillo -- a favorite among players, coaches and other staff -- after the veteran starter was traded to the White Sox on Saturday night.

Domínguez was the key return in that deal, which also included Minor League outfielder Nolan Jones, catcher Boston Smith (Mariners No. 14 prospect) and cash considerations.

"For me, I always tried to be a good person to everyone on the team -- a good person and good teammate,” Castillo said through an interpreter, before Seattle’s series finale vs. Minnesota on Sunday. “Just thanking everybody in the organization for always treating me so well."

Castillo was never the rah-rah or emotional fixture in Seattle -- but the 33-year-old was a legitimate leader. He just went about it in a more under-the-radar way.

“He knows how to relate to everybody,” Logan Gilbert said. “I think that's a really rare thing to see, but especially on the pitching side of things. He did more for me and other people than fans will ever realize.”

Indeed, Castillo’s impact on the rest of the Mariners’ rotation -- all homegrown and young starters aside from himself -- was more profound than most might think.

“Especially my rookie year [in 2023] and and in '24, I kind of leaned on him a lot,” Bryce Miller said. “Like, between starts, I kind of learned a lot watching him. And he's one of those guys that's just extremely consistent. Like, whenever things are going good or when things are going bad for him, he's the exact same guy every day. And so that was something I tried to take from him, and it's not always easy.”

Most within the clubhouse knew that Castillo being dealt before Monday’s 3 p.m. PT Trade Deadline was a legitimate possibility. The club had been operating with six healthy starters since mid-May and had made it known to other clubs that it was willing to deal from that depth to address other roster needs.

Still, it came to Castillo -- who’s now been traded six times in his career -- as “a surprise.”

“It's hard. Being with a team that you've been here for so long, it's tough," Castillo said. "But it's part of the business. You're here one day, and then you don't know where you're going to be tomorrow.”

Looking ahead, the Mariners will now truncate to a five-man rotation -- featuring Gilbert, Miller, Emerson Hancock, Bryan Woo and George Kirby, who remained on turn Sunday in the wake of his name also cropping up in trade talks.

Kade Anderson, MLB Pipeline’s No. 5 overall prospect, will likely be in the mix down the stretch, too -- but when and how remains both unclear and one of the club’s biggest intrigues heading into the final two months.

As for Domínguez, he’ll be immediately injected into a late-innings relief role -- and give manager Dan Wilson more leverage depth.

This is Domínguez's eighth season, and he also has 29 games of playoff experience with three teams -- including last year’s Blue Jays, with whom he pitched in the World Series.

“He'll bring a lot on and off the field, I think, for us,” Wilson said, “and that's awesome.”

Moreover, the Mariners are anticipating three key relievers returning from the injured list in the coming weeks -- including setup man Matt Brash, flamethrower Carlos Vargas and their most versatile bullpen arm, Cooper Criswell.

“Your bullpen really starts to take shape, and you have a lot more versatility, a lot more options,” Wilson said. “And that's really exciting as we get ready to go down the stretch here.”

In the interim until Domínguez arrives, left-hander Josh Simpson was recalled from Triple-A Tacoma on Sunday, as the Mariners had an open 26-man roster spot after trading Castillo.

And there could be more moves to come, as Seattle is still actively seeking a right-handed bat, and presumably, will seek more avenues to beef up its bullpen.