This was merely a live batting practice session of about 25 pitches Tuesday, but it brought something that has been in scant supply around the Mets this season.

A positive vibe.

Matt Harvey threw off the mound to Brandon Nimmo and said after initial rust that he felt great. Now the Mets didn’t rush out to align their playoff rotation, but at least this was a case of a pitcher returning from and not leaving with an injury. Harvey, along with manager Terry Collins, expressed optimism he will pitch again this season. In fact Harvey said he would “probably do a rehab start” within “the next week or so.”

“Felt great. It’s nice to get on the mound again and then obviously do my first live batting practice,” said a slimmed-down Harvey. “It was obviously a little rusty at first but towards the end, I was able to get the ball down and finish the pitches the way I wanted to and see the ball flight. Everything felt great.”

Harvey, who underwent surgery for thoracic outlet syndrome in July last year, has been on the disabled list since June 16 with a stress injury to the scapula bone in his right shoulder. Tuesday was a baby step in the return process.

There will be more sessions like Tuesday’s when Harvey threw 25-30 warm-up pitches and then his 25 to Nimmo. There will be rehab games. But there has been progress that should let Harvey start again this season.

“That’s why we’re doing what we did today. My goal is to get back out there as soon as I can,” said Harvey, who was 4-3 with a 5.25 ERA in 13 starts before going on the DL. “Obviously, health — and performance — is the biggest thing, so I’m on track to get back hopefully pretty soon.”

Patience may be a virtue but it is not part of a baseball fan’s makeup. And concerning Harvey pitching, they want to know “when?”

“No one has an answer for that,” said Collins. “He’s just got to continue to build up his arm strength and all the muscles involved in throwing. … I don’t know how many times he’s got to face a hitter before he goes and starts pitching in a rehab assignment. He’s got a ways to go.

“I think you’ll see Matt back on the mound this year. But when? I don’t think there’s a timetable … but I know he’s bound and determined to come back. He’s driven and he wants to get back on that mound.”

Harvey wants a return for all the obvious reasons, and for peace of mind heading into the offseason.

He threw with full intensity Tuesday — “I got after it pretty good,” he said — and used all of his pitches. Yes, it was only batting practice but it was a positive step.

“My arm can work the way that it’s supposed to,” Harvey said. “The strength program that we did for the back of my shoulder and the scap area, now it’s moving the proper way. I was talking to [pitching coach] Dan Warthen the other day when I came back from Florida and I said I was excited because it was finally fun to throw a baseball again.”

Catcher Travis d’Arnaud watched Harvey throw.

“The ball was coming out great. He looked effortlessly fast. All his pitches are sharp,” d’Arnaud said. “He did a good job.’’

Nimmo, stressing he never batted against Harvey before, liked what he saw.

“His fastball had good life. His changeup was good. His slider was sharp. Then it all comes down to location. He located really well, got more comfortable as the bullpen went on,” Nimmo said. “He knows what he’s capable of. It’s just getting that feel from taking time off.”

There remains a long path ahead, but there is renewed strength in his shoulder.

“It was difficult playing catch a while ago and felt like it was always an uphill battle,” Harvey said. “I knew something wasn’t right but I tried to fight through it and we came to figure out that the shoulder was just really weak and there was a lot of nerve issues causing the muscles not to respond very well. The time off helped and obviously the strength program helped and everything feels great now.”