Mets designated hitter DJ Stewart hits a sacrifice fly during...

Mets designated hitter DJ Stewart hits a sacrifice fly during the third inning of a game against the Dodgers in Los Angeles on Friday. Credit: AP/Ashley Landis

SAN FRANCISCO — DJ Stewart, who made the Mets only by default and perhaps on a temporary basis coming out of spring training, has since become one of their most productive hitters.

But now  he faces what likely will be a greatly reduced role when J.D. Martinez joins the team, maybe as soon as Friday.

The arrival of Martinez, a perennial All-Star and widely respected hitting savant/slugger, figures to bolster the offense but lock up the DH playing time, erasing the flexibility the Mets have enjoyed at that spot. For Stewart, who has made every case to stay in the majors, it could mean being limited to spot starts and pinch-hit appearances.

“J.D. Martinez is one of the best hitters in this game. I’m not oblivious to that. He’s definitely going to help our team when he gets here,” Stewart said. “But I think I can do that as well. I can definitely help this team. I proved that last year. I think I’m showing that now.”

That confidence represents a total turnaround from Stewart’s mindset early this month, but it is hard earned.

Entering the Mets’ series opener with the Giants on Monday night, he was first on the team in OPS (.985), slugging percentage (.559) and OBP (.426), third in homers (three) and tied for fourth in RBIs (10).

All that even though he went hitless for the first week and a half.

 

How about that for early-season role-related whiplash?

“It’s been, honestly, a lot,” Stewart said.

Flash back to late March. The Mets had just signed Martinez, who wouldn’t be ready at the outset. They brought Stewart to New York when camp broke but were straight up with him: He would be on the roster only if they couldn’t find somebody better in the final leadup to Opening Day. On the original timeline, they were going to add Martinez potentially only 10 days into the season, anyway.

When Stewart did end up on the roster, he was (and is) a part-time player, plugged into the lineup primarily against righthanded pitchers.

In the ensuing days, fresh off the vote of minimal confidence from Mets decision-makers, Stewart feared the inevitable: Martinez’s arrival. His performance reflected that.

“I was letting that affect how I was playing,” he said. “You’re obviously coming here trying to do your job, you try to block out the outside stuff, but it’s honestly tough.

“Then when you’re not feeling as great and you know there’s a ticking time [bomb], you try to do too much. ‘My swing doesn’t feel great, but I need to produce right now.’

“Whenever you try harder in baseball, it doesn’t always work. This is one of those sports that the harder you try, it usually goes the other way. I was letting that dictate — I was living and dying with each at-bat. And I’m not doing that now.”

He got over it by enduring the vicious cycle that ends any skid: pregame preparation, which fostered confidence, which was followed by a couple of hits falling in, which bred more confidence, and so on. He got hot around the time Martinez shut down briefly because of lower-back tightness.

Also, Stewart said, it helped that manager Carlos Mendoza offered a series of chats about his expectations, including when he was  slated to play.

“Mendy has done a good job of communicating with me and telling me to relax and have fun,” Stewart said. “That’s what I was doing last year: Just having fun, enjoying the game. Now I’m doing that again. That’s why the turnaround has come.”

Mendoza said: “The one thing I’ll tell everyone in here is control the things you can control. DJ has been a huge part of this team. I could see a spot for DJ even when J.D. comes back. These are some of the conversations we’re going to start having here pretty soon.”

Stewart leads the Mets in DH starts with 13. Starling Marte (four), Francisco Alvarez (two), Brandon Nimmo (two) and Tyrone Taylor (one) also have seen time there.

But that will be Martinez’s job soon.

“I don’t know what that means for me,” Stewart said. “Right now I’m living in the present, trying to play the best baseball that I can. I’m going to try to do that all year long.”

Notes & quotes: The Mets restocked their bullpen by activating righthander Sean Reid-Foley (right shoulder impingement) from the injured list and calling up lefthander Josh Walker from Triple-A Syracuse. They designated Michael Tonkin for assignment and sent Grant Hartwig back to Syracuse . . . Tonkin has been DFA’d three times in a half-month — twice by the Mets, once by the Twins. “It’s not easy,” Mendoza said. “It’s not the fun part of this job.” . . . Kodai Senga (right shoulder strain) is scheduled to throw two bullpen sessions this week, then will advance to facing batters.

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