Of course, Andrés Muñoz says, he loves to throw hard. He loves the feeling of unleashing a triple-digit fastball, popping the catcher’s mitt and watching the swing-and-miss reactions of opposing hitters.

“Beautiful,” he called it.

No pitcher in Mariners history has thrown faster than Muñoz, a 23-year-old right-hander from Los Mochis, Mexico. Twice last month Muñoz hit 103 mph on the radar gun — 103.0 against Texas on July 16 and 103.2 against Houston on July 24 — and he owns the 12 fastest pitches in club history during the Statcast era (since 2008), all thrown this season.

But in today’s era of whiplash velocity, it takes more than the fastest fastball to be one of the most untouchable pitchers in the game.

So as the Mariners have leaned more and more on Muñoz in the biggest moments, against the best hitters, Muñoz has leaned more and more on a slider that has become one of the single best pitches in all of baseball.

Beyond Muñoz, the slider has been so effective out of Seattle’s bullpen that it’s not a stretch to suggest that it alone could be as important as any other factor in the Mariners’ push for their first postseason appearance in two decades.


Collectively, the Mariners’ top six relievers — Muñoz, Paul Sewald, Erik Swanson, Matt Festa, Diego Castillo and Penn Murfee — are throwing sliders on 50.3% of all their pitches while holding opponents to a .163 batting average with that pitch.

“This is why you play the game, right? You play to get to the World Series,” Swanson said. “To have the opportunity play meaningful games here the last two months is really special, and I feel like we have the bullpen to be able to get us there.”

Since June 21, the Mariners bullpen ranks No. 1 in the majors in ERA, opponents’ batting average and walks-plus-hits per inning.

The Mariners already had one of MLB’s best bullpens in 2021, and manager Scott Servais said the club was “cautiously optimistic” Muñoz would emerge this season as a reliable addition, two years removed from Tommy John surgery.

Muñoz’s production has surpassed any reasonable expectations.

Muñoz ranks first among all pitchers in the American League with a strikeout rate of 40.1%, with 69 strikeouts in 45 innings. He’s allowed just two runs his last 24 2/3 innings dating back to mid-June, allowing just nine hits and five walks with 44 strikeouts in that stretch.

He’s doing it with that devastating two-pitch mix: a fastball with an average speed of 100.1 mph (second in MLB behind Minnesota’s Jhoan Duran, 100.6); and an 87.8-mph slider that he’s throwing 60.8% of the time.


Opponents are hitting just .122 off his slider this season (12 for 98).

“When I go out there, I have the mentality that I’m going to strike the whole world out,” Muñoz said through interpreter Freddy Llanos. “Obviously, that’s not always possible. I just try to do my job and try to get out of the inning any way possible.”

In Tuesday’s epic 1-0 victory over the Yankees, Muñoz pitched a perfect ninth inning to preserve a scoreless tie, striking out the top three batters in the New York lineup on 15 pitches. Of the seven pitches he threw to Aaron Judge, six were sliders; Judge swung and missed at a 3-2 slider for the second out.

Muñoz struck out Andrew Benintendi on three pitches to end the inning — freezing him with a 102-mph fastball on the inside corner — and then gave a subtle double fist pump as he walked back to the dugout.

“Those are huge for young players to get through those moments and succeed and build upon that going forward,” Servais said. “We have a ton of confidence in him. He’s got a lot of confidence in himself. He doesn’t really carry himself that way, but it’s growing. It’s growing day by day.”

Muñoz’s breakthrough is drawing comparisons to Edwin Diaz’s emergence out Seattle’s bullpen in 2016-17.

Like Muñoz, Diaz relies on a 100-mph fastball and a wipeout slider that make him almost impossible to hit at times. (Diaz, part of the ballyhooed Robinson Cano trade to the New York Mets in 2018, has been so dominant this season that he’s starting to generate some Cy Young buzz.)


“We’ve always compared him to Diaz,” Swanson said. “They’re very similar, hard-throwing guys. And they both throw a lot of strikes.”

Sewald played with Diaz in New York for parts of two seasons, and has watched Muñoz’s ascent this year.

“Their stuff is pretty similar,” Sewald said. “(Diaz) maybe has a little more rise on his fastball and throws it up in the zone. But ‘Muny’ finds a way to blow it by people throwing it right down the middle.”

On 14 occasions this season, Muñoz has struck out at least three batters in relief. Only one other reliever has done that this year — Diaz.

“Obviously, he’s a guy I look up to and a guy that, when I see him, I tell myself, ‘I want to be like that pitcher,’” Muñoz said.

MLB pitching leaders in strikeout rate this season

1. Edwin Diaz, NYM, 52.9%
2. Devin Williams, MIL, 41.2%
3. Ryan Helsley, STL, 40.9%
4. Josh Hader, MIL/SD, 40.6%
5. Andrés Muñoz, SEA, 40.1%

Source: FanGraphs (through Aug. 10 games)