This story was excerpted from Daniel Kramer’s Mariners Beat newsletter. To read the full newsletter click here. And subscribe to get it regularly in your inbox.

The turning point for Diego Castillo was around one month ago, and the Mariners have sorely needed it. Seattle's leverage reliever is back to thriving in those moments, going scoreless in 11 of his past 12 outings, including nine straight. Since locking down a big win in New York by retiring Mets slugger Pete Alonso with the bases loaded on May 15, everything has been clicking for the fifth-year veteran.

"It feels good. People that know me in this league, they know what kind of situations I'm putting into this game, so that's me and I feel good about it," Castillo said through an interpreter.

In this stretch, opposing hitters are just 3-for-40, all singles, with three walks and 18 strikeouts for a .215 OPS and a 0.49 WHIP. His 0.7 WAR figure, per FanGraphs, is the Majors' highest among relievers during the span.

"It's the sharpest we've seen Diego in a long time," manager Scott Servais said. "His confidence is back and putting him in those high-leverage moments, he thrives in those. But he's executing pitches."

Castillo still has a 5.09 ERA on the year, but his expected ERA, which is based on quality of contact (exit velocity and launch angle), plus strikeouts and walks, is 2.78, nearly identical to his 2.79 xERA in 2021 and 2.86 xERA in 2020.

Castillo's resurgence can be credited to numerous factors, but the most notable appear to be that 1) his slider is back to its elite form, landing for strikes and generating a ton of swings and misses, 2) his fastball velocity is on the rise and 3) he's ahead in counts far more often.

Here's a breakdown of each:

• Castillo has always had above-average stuff, but his slider can be particularly susceptible when he loses feel for it, which leads to less movement and makes it far easier to read. Opposing hitters were 8-for-31 on the slider before his big game in New York and are 1-for-27 against it since -- including that huge punchout of Alonso. Moreover, when hitters are making contact, it's typically weak, as Statcast shows:

• The righty's sinker velo has increased, up from 94.8 mph to 95.1 mph in the past month, which is always a positive.

• It always helps to pitch ahead, and Castillo has found himself in more favorable sequences early. In 0-0 counts, Castillo has landed strikes 66.7% of the time, up from 58.2% prior. For the season, when he's ahead in the count, opposing hitters are just 5-for-37.

As such, he's begun to regain his grasp on the Mariners' most important late-innings sequences, a role he's relished. Aside from Sergio Romo, Castillo is the only reliever in Seattle's bullpen that has postseason experience.

Castillo by leverage in 2022
High: .167/.222/.167 (.389 OPS)
Medium: .222/.263/.222 (.485 OPS)
Low: .283/.365/.391 (.757 OPS)

"I don't think Diego ever lost faith in himself or trust in his stuff, whatever you want to call it," Servais said. "It was just a matter of executing and feeling good about what you're doing out there. And he certainly feels good about what he's doing now. You can see it, he's kind of got the strut back on the mound. He's doing his little thing, all those little quirky things he does with the hat and the glove and everything else. I love seeing it."

There's also a confidence factor here, too. Castillo's worst outing of the season was just before this recent run, on May 7, against a Rays team that signed him as an international free agent as a 20-year-old in 2014, when he surrendered a career-high five runs.

"Diego has been the Diego that everyone has seen over the last five Major League seasons," reliever Paul Sewald said. "And he's not going to let one bad series against his former team dictate what kind of season he has."