Mets pitcher Steven Matz throws during a spring training workout...

Mets pitcher Steven Matz throws during a spring training workout on Feb. 18 in Port St. Lucie, Fla. Credit: Newsday/Alejandra Villa Loarca

PORT ST. LUCIE, Fla. — With his command lacking and his confusion mounting, Steven Matz stuck with the pitch that wasn’t working: his curveball.

The split-squad Mets lost to the Red Sox, 9-3, in a Grapefruit League game at First Data Field on Monday, and Matz lasted only 2 2⁄3 innings, about an out shorter than planned after he reached his 50-pitch limit.

But to Mickey Callaway, the greatest takeaway from the Long Island lefty’s day was his willingness to stick with the pitch that was failing him — as well as what that says about Matz’s growth as a pitcher and his improved standing in the rotation relative to spring trainings past.

“He’s growing up,” Callaway said. “He probably would not have done that last year. He would’ve been worried about the result. He’s worried about getting better.”

Matz faltered early, drawing a visit from pitching coach Dave Eiland, who asked about the curve. He told Matz to get the breaking ball in the dirt when he had a hitter 0-and-2 — feel free to waste a pitch just to see if the batter will chase — and Matz at least tried. He twice attempted to bury an 0-and-2 curve, but each time it hung up in the zone and turned into a hit.

“I kept wanting to keep going back to it because I didn’t like the way I was not commanding it,” he said. “Just kept going back to it, and that’s part of spring training. You got to use stuff now even if you don’t have it.”

Matz didn’t know why his curveball, which he said felt sharp in his debut last week, wasn’t working. Maybe it was his release point, he said. Maybe it was his arm strength. Either way, he has time to figure it out and straighten it out — or unstraighten, since it’s a curveball — the next three weeks.

“It’s something I know I have to address,” Matz said. “That’s what spring training is for.”

For Matz, such a sentiment is a luxury. At this time last year, he was coming off an injury-plagued half-season and competing for a spot in the back of the rotation. As much as spring training results do not predict regular-season performance, they did matter to a certain extent for Matz in 2018.

Then he won a rotation spot, stayed healthy and made 30 starts for the first time. That turns this spring into a time to experiment, not stress over results.

“He deserves to be able to come into this spring training and do everything he can to get himself ready for the season,” Callaway said. “It’s not always like that when you’re battling for a spot, and it makes it tough and you feel like you have to execute every pitch. Sometimes that can hinder your development. Right now, he doesn’t have to feel that way. He can go out there and relax, work on things and make sure he’s in the best spot possible on Opening Day.”

Did the curve get better the longer Matz pitched Monday? Nope, he said. But his other pitches were fine, good enough for him to call it “a step in the right direction” despite the five hits, four runs and two walks.

Matz has earned the right not to care about his linescore at this point on the calendar.

“He was working on his craft and trying to get better,” Callaway said. “I thought that was really impressive out of Matzy, to be able to be out there competing . . . to be able to slow everything down and think like that.”

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