SAN DIEGO -- Of the 43 appearances (and 38 starts) that Zebby Matthews had made as a professional pitcher entering Monday, he had never allowed three free baserunners to reach on his watch. That’s the sort of thing that happens when issuing walks simply isn’t something you do.

But the series opener between the Padres and Twins entered uncharted territory when the rookie right-hander not only hit Luis Arraez to begin the game, but then walked two batters -- gasp -- in the third inning.

All three of those free baserunners ultimately came around to score, and they turned out to account for the difference in the Twins’ 5-3 loss to the Padres at Petco Park on Monday night in Matthews’ second big league start. It should say something about his reputation that so early in Matthews’ career, a two-walk outing bordered on cause for alarm for outside observers.

“Everybody's human,” Matthews said. “As much as I try and go out there and not walk guys and make them earn it on base, it's going to happen at some point. … It's not something I put too much pressure on myself on. Obviously, I'm not happy with the two walks or the hit batter. But at the end of the day, you've just got to move on and learn from it.”

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It’s a start that put the 24-year-old into the loss column for the first time, but also an outcome that wasn’t necessarily reflective of how Matthews pitched. He allowed only four hits across five innings, with rookie Jackson Merrill’s three-run double serving as the only hit in the pivotal third inning.

All three of those runs were unearned because of the two-man miscue that started it all. First baseman Carlos Santana was unable to handle Jurickson Profar’s sharp grounder to the right side. Then, after second baseman Edouard Julien recovered the ball and threw to first, Matthews wasn’t able to snag the ball while covering the bag.

That led to the two walks to Jake Cronenworth and Xander Bogaerts. With two outs, Matthews got ahead of Merrill -- who’s in the midst of a stellar rookie campaign -- on an 0-2 count before leaving a changeup belt-high that got blasted to the gap in left-center to clear the bases.

“One-pitch mistake, and we paid [for it],” catcher Christian Vázquez said. “Needed to go fastball there again. Matthews has a great fastball, and we learn from that.”

As the Twins move forward with their three-rookie rotation, involving Matthews lined up alongside David Festa and Simeon Woods Richardson, that third inning will serve as another episode in Matthews’ continued on-the-job learning as he navigates a dizzying season that saw him elevated from High-A to the Majors in just over three months.

Matthews issued seven walks all season in 97 Minor League innings before his callup to the Twins, and he made it through his five-inning big league debut against the Royals last Tuesday without issuing a free pass.

If there’s such a thing as throwing too many strikes, Matthews’ extreme strike-throwing skillset perhaps puts him in the best position to show the potential pitfalls -- and he pointed to that pitch against Merrill and other two-strike offerings from his outing as continued elements of his work this season on actually better being able to leave the strike zone when needed.

Matthews said that 0-2 pitch to Merrill was meant to be a chase pitch beneath the strike zone -- but it hung up.

“It's something we've been working on all year, being better with [two-strike] execution,” Matthews said. “It's something that I'm going to continue to work on, I think, for a while. Always trying to throw stuff in-zone, not trying to walk guys, make guys earn it on base. It comes with a price there.”

This certainly isn’t a phenomenon unique to Matthews on the Twins’ roster. Pablo López, who has similarly been an aggressive strike-thrower, with 152 strikeouts and 32 walks this season, has pointed to his struggles in expanding with two-strikes as part of his struggles. Fellow youngster Louie Varland, another extreme strike-thrower, has been impacted by the same.

One big mistake was all -- but Matthews paid the price.

“Zebby’s such a good strike-thrower -- he’s a guy that relies on that for a key to his success,” Twins manager Rocco Baldelli said. “Today, the command of his pitches and the feel for his pitches was probably just a little bit off.”