J.D. Martinez watched from Port St. Lucie as the Mets got off to an 0-5 start and had one thought as he tried to get back to the majors after signing with the team in late March: “Hurry up.”

That helped result in a recurrence of the lower-back tightness Martinez has dealt with since 2019, but he’s confident the cortisone shot he received will take care of the issue.

“I got one last year and it never came back,’’ Martinez said before making his Mets debut on Friday night against St. Louis at Citi Field.

It’s been a longer wait than anticipated for the 36-year-old, who has remained one of the top hitters in the game when he’s healthy.

Martinez called missing nearly the first month of the season “obviously frustrating.”

Now he adds a right-handed bat that Carlos Mendoza deployed for the first time on Friday, hitting fifth, right behind Pete Alonso.

“It feels good writing the lineup and putting his name in,’’ Mendoza said. “But I don’t think it’s fair to put that pressure on him and say, ‘OK, we’ve got J.D. now.’ He makes our lineup a lot deeper, but we have a lot of good hitters here.”

Mendoza added he will be “mindful” about giving Martinez time off, but doesn’t have any rules about resting the slugger, who missed nearly three weeks with the back injury last year, as well as another stint on the injured list in August due to a groin injury.

Some members of the rest of the lineup aren’t performing up to their usual standards and the Mets are hopeful Martinez makes everyone better.

“There are good hitters in this lineup,’’ Martinez said. “They struggled early and got things going later. These are all really good players: [Francisco] Lindor is not gonna hit what he’s hitting [now]; [Brandon] Nimmo isn’t gonna hit what he’s hitting. It’s the law of averages.”

Martinez played just three minor league rehab games after returning from his back injury and said he wants to get his timing back while in the majors as opposed to spending more time getting ready at Triple-A Syracuse.

“My body feels good,’’ Martinez said of why he believed he’s prepared to contribute in the majors. “There’s nothing like facing big-league pitching. I’ll try to grind through here and help as much as I can and get my bearings.”

His new teammates are looking forward to it — including the ones that have had to face him in the past.

Luis Severino has seen first-hand how dangerous Martinez can be.

Martinez is 10-for-22 with a pair of doubles, a homer and an OPS of 1.160 versus the right-hander, numbers Severino is well aware of.

“As a pitcher, I have my sequences, and I know he’s one of the smartest guys at the plate,’’ Severino said. “He watches a lot of video and he’s got a great approach. I can get to two strikes against him, but after that, it’s hard. We’ve battled.”

And he believes Martinez will be the same in Queens.

“His presence changes a whole lineup,’’ Severino said. “He’ll protect Pete and give him better pitches to hit. It’s gonna be fun.”