PORT ST. LUCIE — Noah Syndergaard might as well have been making his first start of the season Thursday.

Throwing live batting practice — with Mets minor leaguers taking swings — the fireballing righty turned heads during a 25-pitch session.

“That ball is moving two feet,” manager Terry Collins said near the batting cage, as Syndergaard strutted his stuff.

Syndergaard seemed amazed with his performance.

“Overall my body feels great,” he said. “I wish I really knew the answer to why I feel like I’m already in midseason form. I just think it’s the fact I threw so much last year and we went so much farther than a normal season or anything we’re used to.

“That short time off didn’t allow my body to really break down or lose muscle memory or anything to my mechanics, but my body feels good, everything was working today. I am kind of shocking myself a little bit how good I feel so early in spring training.”

Syndergaard has begun throwing a slider — he says some days it acts like a cutter — to complement his fastball, curve and changeup.

“I started toying a little with it last year and actually during the World Series I started to throw it more and it clicked somehow,” Syndergaard said. “It’s another thing I don’t have the anwser for, but something really clicks and it really helped me and part of my success during Game 3.”

After indicating he wasn’t a fan of Yoenis Cespedes wearing his cap backward in the batting cage and might address the matter, Collins said he won’t ask the outfielder to change anything.

“In years past those kind of things start issues, so I’m going to ignore,” Collins said.

Brandon Nimmo, who has a partially torn tendon in his left foot, said he will need at least another two to three weeks of rehab before he can consider starting baseball activities. The outfielder, who is expected to begin the year at Triple-A Las Vegas, sustained the injury on Jan. 18.

“The nice part is [the injury] seems to be a lot less serious than we thought at first,” Nimmo said. “So I’m looking to just get this rehab process done this time and hopefully we’ll have a healthy season and not have to deal with it.”