When the Mariners first acquired Andres Munoz as part of the 2020 midseason trade that sent catcher Austin Nola and relievers Austin Adams and Dan Altavilla to the Padres, the hope was that the hard-throwing right-hander, who was four months into his recovery from Tommy John surgery, would be ready to contribute by midseason.

Unfortunately for Seattle, Munoz, 22, suffered a setback while building up arm strength in his throwing progression in spring training. The Mariners shut him down immediately and decided to be cautious when he resumed his throwing program, removing any plan for a return to the big league roster in 2021.

But in a promising development for the 2022 season, Munoz began a rehab assignment Friday with the Mariners rookie league team in the Arizona League, starting the game and pitching one inning. He struck out all three batters he faced and hit 101 mph on the radar gun. Munoz had been hitting 99 mph consistently in his bullpens leading up to his outing.

“He’s special,” manager Scott Servais said. “I got text messages from a number of different people last night, giving me a thumbs up. He had a great outing in his first time out there. Good for him. Awesome young man. And I say young, he is very young. And the fact that he’s got some majorly experience already under his belt.”

Munoz made his MLB debut July 12, 2019, for the Padres at age 20. He made 22 relief appearances, posting a 1-1 record with a 3.91 ERA. In 23 innings pitched, he struck out 30 batters with 11 walks. Of the 10 earned runs he allowed in those 22 appearances, six came in his final two outings. In his first 20 outings, he pitched 21 1/3 innings with a 1.69 ERA, including 27 strikeouts and 10 walks. According to Statcast data on Baseball Savant, Munoz’s fastball averaged 99.9 mph while his slider averaged 86.5 mph with hitters swinging and missing on it 44 percent of the time.

Per text messages with general manager Jerry Dipoto and director of player development Andy McKay, Munoz will make three more appearances, pitching one inning every four days.

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While four appearances might not seem like a lot, it’s big for the psyche of Munoz and allows him to go into the offseason knowing he’s healthy.

“The big thing for him is he ends the season on a high note,” Servais said. “He gets a couple of rehab outings under his belt, so he feels really good coming into next year. The sky’s the limit with this guy. It is an electric arm. It’s one that I probably compare from my early look at it, kind of what we thought of Eddie Diaz when he first showed up. It’s that kind of electric, 100-mph stuff.”

Munoz isn’t the only reliever recovering from Tommy John surgery that’s expected to be in the opening day bullpen.

Veteran right-hander Ken Giles, who underwent the procedure Oct. 1, 2020, hasn’t reached the point in his recovery where to start a rehab stint. But he’s expected to be ready to go when spring training opens in February.

Munoz and Giles would join a projected bullpen that includes right-handers Paul Sewald, Drew Steckenrider, Diego Castillo and Casey Sadler and lefty Anthony Misiewicz.