SEATTLE -- The Mariners have found their bullpen replacement for Kendall Graveman, as the club acquired Rays closer Diego Castillo on Thursday.

In exchange, Seattle will part with reliever JT Chargois and third baseman Austin Shenton, one of its more coveted prospects.

SEA gets: RHP Diego Castillo
TB gets: RHP JT Chargois, 3B Austin Shenton (Mariners No. 17 prospect)

On paper, this one will probably be much more well-received than the deal that sent Graveman to Houston on Tuesday and left an emotional clubhouse confused at the trajectory of general manager Jerry Dipoto’s Deadline strategy. Though Graveman’s numbers are superior and his veteran leadership and imprint on his teammates can’t be positively quantified enough, Castillo has also been stellar.

The 6-foot-3, 250-pound left-hander has racked up 14 saves, a 2.72 ERA and a 146 ERA+ over 37 outings this year and has been arguably the best reliever for a club loaded with them -- and one that has World Series ambitions for this season.

Speaking of, Castillo also brings October experience having pitched in 11 games during Tampa Bay’s run to the American League pennant last fall, over which he was scoreless in eight of 10 outings. He was also scoreless in each of his four 2019 playoff starts.

The Mariners, who are two games back of the second AL Wild Card, are hoping he will be doing so in Seattle sooner and later. That’s another key component to this deal -- Castillo carries three years of club control, all via arbitration, which could keep him in the mold for the rest of these final stages of the rebuild.

Chargois has been strong, but sources said that Tampa Bay wanted a reliever in return to offset Castillo’s void. And the club coveted Shenton, whose inclusion pushed the deal to the finish line. Shenton, who was recently promoted to Double-A Arkansas, is hitting .300/.414/.566 (.980 OPS) with 12 homers and 61 RBIs this season. He is talked about in prospect circles as one who could rise rapidly.

“Ultimately, we arrived at Austin Shenton, which was painful for us,” Dipoto said. “We really like Austin. He can really hit. He's a great kid. But you have to give to get, and I've said all along that we were focused on doing what we could to improve our team now and to continue to improve our team for 2022 and beyond.”

Despite losing Graveman, who will be a free agent at season’s end, and Chargois, who signed a Minor League contract as a non-roster invite to Spring Training, the Mariners have positioned themselves with a strong relief corps heading into 2022, including former All-Star Ken Giles and 104-mph flamethrower Andrés Muñoz, both of whom are out for ’21 but have progressed to a throwing program.

“It is formidable on paper, and I know we're excited about it,” Dipoto said. “We still have two months of this season to play. So we're hopeful that this group can be as formidable, but we’re anticipating Andrés Muñoz and Ken Giles joining this group in ‘22 and it’s pretty exciting, because right now all the group that is down there now projects to come back for 2022.”

Dipoto also addressed the uncomfortable timing of dealing Graveman on Tuesday, less than 24 hours after arguably the biggest win since the rebuild began, and to the division-rival and first-place Astros, who Seattle trails in the AL West.

"[Tuesday's] deal was it had to be made on [Tuesday], because Rafael Montero needed to be placed on waivers by [Wednesday]. So there was no way to execute that deal on any day other than [Tuesday],” Dipoto said. “It felt wonky. I feel badly for that. But it had to be done that day if we were going to do it. And [today's] trade was the next part of that. ... We felt like there was a chance that we could get this across the goal line, and today it really picked up."

What’s also picked up are the teams that the Mariners will be competing against for a Wild Card spot, assuming they don’t catch Houston in the AL West. The Yankees added elite left-handed sluggers Joey Gallo and Anthony Rizzo. The A’s added outfielder Starling Marte and reliever Andrew Chafin. While Dipoto acknowledges -- and figured -- that the teams around Seattle would get better before Friday, he is committed to the approach of not mortgaging the most premium prospect capital in their No. 3-ranked farm system.

So after Thursday’s trade, which Dipoto all but assured earlier this week, are the Mariners done? They still have a need for a right-handed infield bat, but the urgency isn’t as high as it was before it acquired Abraham Toro in the Graveman deal. Toro has already homered in each of his first two games.

“Hope so, but we're not going to empty the coffers to try to keep up with what others are doing on Trade Deadline day. ... As the week has gone on the, you know, the prices appear to be getting more reasonable, which is typically the case,” Dipoto said.

“If we can add another bat to this club, we're going to be pretty active in in the hours ahead to see if we can do that. And again, we're doing what we can do to make sure that we are as good as we can be in ‘21, while not taking away any meaningful part of what we're doing building for the future.”