J.D. Martinez at news conference during Mets spring training.

J.D. Martinez at news conference during Mets spring training. Credit: Newsday/Tim Healey

SAN FRANCISCO — In a way, the Mets are about to celebrate Opening Day all over again.

J.D. Martinez is slated to make his Mets debut on Friday when they play the Cardinals to start a seven-game homestand, manager Carlos Mendoza said Wednesday morning.

Martinez had one last box to check — a second appearance with Triple-A Syracuse later Wednesday — but if that went fine, the Mets finally would add to their lineup their only major offensive addition of the offseason.

Mendoza said he plans to bat Martinez, a righthanded-hitting DH, behind Pete Alonso, which would be fifth if the Mets stick with their recent order.

“We have a lot of really professional hitters here,” hitting coach Jeremy Barnes said. “But in general, he may be one of the most in the league.”

Mendoza said: “I’m really looking forward to it. This is a guy who — it’s not a secret — how good of a career [he has had], what he provides from the offensive side, the impact that he has on the ballclub. This is a pretty smart hitter. He’s got his ideas. He’s very impactful for the position player group side of things. I’m really looking forward to having him on the team.”

Martinez, 36, won’t be a literal everyday player, at least not immediately. His monthlong ramp-up lasted that long because of a bout of lower back tightness, a problem that has plagued him for years. He and the Mets agreed to a one-year, $12 million contract on March 21, a week before the season began.

Between Martinez’s physical condition and his personalized, abbreviated spring training, Mendoza doesn’t want to ask him for too much too soon.

“This is something that I’ll have a conversation with him [about], but out of the gate, I’m not going to run this guy and DH him every day,” Mendoza said. “He’s going to need some days. It’s one of those where I’ll sit down with him and put together a game plan here. It’s important. He’s too valuable for this team. We gotta take care of him.”

Extra bases

Starling Marte said he was fine after a pitch nipped one of his fingers on a bunt attempt in the 8-2 win over the Giants . . . Adam Ottavino’s walk of Jung Hoo Lee was his first of the season. He has a 1.86 ERA . . . The Rangers claimed lefthander Kolton Ingram off waivers from the Mets.

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