Armed with belief, 'electric' fastball, Isaac Mattson making impact on Pirates bullpen

When the Pittsburgh Pirates talk about Isaac Mattson, the first thing they mention is his electric fastball. The 29-year-old right-handed reliever throws his four-seamer on 72.2% of his pitches, leaving batters befuddled as the ball disappears.

Mitch Keller marveled over Mattson’s heater after he recorded three strikeouts — all swinging — in 1 1/3 innings against the New York Mets, in what has become a familiar refrain over the past month.

“I don’t even know if we need to call anything other than his fastball right now,” Keller said. “He’s just got a stupid fastball that’s missing bats. … That’s the one that guys go back to the dugout and be like, ‘It looks great. I just can’t hit it.’ ”

Mattson has morphed from minor leaguer to high-leverage reliever this season, and the Pirates used him in key situations their past two games.

Despite giving up a pair of walks, he preserved a shutout with a scoreless eighth inning to earn the victory in Tuesday’s 1-0 win over the St. Louis Cardinals. On Wednesday, Mattson had Jose Fermin twisted into a corkscrew with a strikeout on a fastball in the ninth inning, then overcame a single and a walk to get the final out in the 5-0 win.

Pirates manager Don Kelly is as impressed with Matton’s journey as he is with his arsenal. A native of Harborcreek in Erie County, Mattson played at Pitt, was drafted in the 19th round by the Los Angeles Angels in 2017 and made his major league debut with the Baltimore Orioles in May 2021. When his mother, Debra, took her own life that July 14, on his 26th birthday, it sent Mattson spiraling.

Mattson mentions his mother, who battled depression, as the “biggest person in my life” and the inspiration for his career.

“Just knowing that she believed in all of us, we tried to do our best in the things we were passionate about,” Mattson said. “That belief has continued to carry me through.”

It hasn’t been easy. A year after her death, Mattson was released by the Norfolk Tides and finished that season with the independent Washington Wild Things. He pitched for the Southern Maryland Blue Crabs of the independent Atlantic League, then signed a minor league contract with the Minnesota Twins. Mattson elected free agency in November 2023 and signed with the Pirates, where his career took off. He was the pitcher of the year at Triple-A Indianapolis and appeared in three games for the Pirates after a late September call-up.

“Talk about a story,” Kelly said. “From Erie to be able to have the success he’s had, just a great job. He’s got great stuff, and he continues to get better.”

Mattson started the season at Triple-A Indianapolis but has been outstanding for the Pirates since he was recalled June 7. He earned his first MLB win that night with a scoreless seventh inning in a 2-1 victory over the Philadelphia Phillies.

His numbers have been superb: Mattson is 2-0 with a 1.62 ERA, 0.78 WHIP and 17 strikeouts against six walks in 16 2/3 innings over 13 appearances for the Pirates. Opponents are batting .133 (4 for 30) against Mattson’s fastball, which is drawing a 26.6% whiff rate.

“With the heater, I feel like I’ve got four different pitches,” Mattson said. “You’ve got up, down, in, out, so being able to use that to good spots, depending on who’s up at the plate. Then being able to sequence it well with the other pitches when I need to and let things work out the way they do. … Knowing that it’s a good weapon for me and hearing those things continues to build confidence in the usage.”

That was evident when Mattson faced 2018 National League MVP and two-time batting champion Christian Yelich in an epic 11-pitch at-bat in the eighth inning of a 5-4 win at the Milwaukee Brewers on June 23. Yelich hit a two-run home run in his previous at-bat in the seventh inning. Mattson threw Yelich 10 four-seamers, and Yelich fouled off five of them before going down swinging at a belt-high 97.3-mph heater.

“The at-bat against Yelich in Milwaukee was an electric at-bat,” Kelly said. “He didn’t back down, Yelich didn’t back down and Issac ended up getting him. … He just has that ability to slow things down in the moment.”

That’s a trait Kelly noticed in spring training, during a Grapefruit League game against the New York Yankees in Tampa after Mattson returned from paternity leave after the birth of his son. Mattson opened eyes by recording four strikeouts in two innings, including Oswald Peraza and MVPs Aaron Judge and Cody Bellinger in the seventh.

“It was electric,” Kelly said. “I mean, the stuff was just flying out. The way he threw the ball and the competitor that he is … I don’t know what it was, but it looked even better and that’s the way he’s been throwing here. The fastball had a little more behind it.”

Mattson has found more meaning in his baseball career and feels like he’s learning something new with each outing. His newfound confidence isn’t by accident. Mattson has focused on his belief in himself.

“That’s my word for this year,” Mattson said. “Definitely I’ve had people, especially in this organization, that have believed in me from the beginning. Having that belief and that confidence helped me to continue to build. Obviously, there’s still work that needs to be done on a day-in, day-out basis, but knowing that I’ve got a team that believes in me and it’s not just me doing it out there on my own, it’s nine of us out there, that means a lot. That’s definitely been a big piece of it.

“Just knowing that I’m here, that I belong here and I can continue to help this team win baseball games, that’s definitely something that I can continue to build off of and continue to contribute.”