PORT ST. LUCIE — Each day another hurdle is cleared. Each day Zack Wheeler lets out a big sigh of relief.

Wheeler pitched Friday against the Braves and came through his initial two-inning stint fine, but it was the next two days that really concerned him, Wheeler told The Post on Sunday.

“How I did the other day reassures me I can get big league guys out. [Saturday] and today my arm feels good, so I am bouncing back,’’ Wheeler said after throwing at the Mets complex. “That’s big. If all stays on course as it is right now, I’ll be ready.

“Just getting back out there is the biggest thing. It sounds dumb, but it’s good just to be back out there, arm feeling good. There have been times that I have thrown and I felt a little something in there [this spring] and I wondered how it was going to feel the next time I threw, but the other day it felt fine and the same for these two days.

“That’s a big relief,’’ Wheeler said. “Everything is starting to be a big relief, honestly. Going out there [Friday] and pitching, big relief. [Saturday] and today, throwing, big relief, today feeling great, knock on wood, big relief.

“I just hope this all keeps continuing going upward.’’

There are a lot of tests going on in Camp Comeback — some have not gone the Mets’ way, like David Wright’s inability to throw — but some tests give the Mets hope for success, like Matt Harvey coming back from thoracic outlet syndrome surgery and Jacob deGrom’s arm strength bouncing back following ulnar nerve surgery.

Wheeler is the most difficult comeback among the pitchers because there have been so many stops and starts since undergoing Tommy John surgery nearly two years ago.

There is so much at play here, and not just physically. Wheeler, 26, has to regain the mental edge, believing he is better than the hitter he is facing, that nothing can stop him in his long road back.

That is the challenge he is facing, beyond his right elbow holding up through all this. His confidence has to be rebuilt, just like his arm was.

Even if Wheeler passes all his tests, it’s likely he will wind up in extended spring training when the Mets break camp to keep his innings down and not have him face the rigors of coming out of the bullpen.

“I’ve been away for two years. I just want to be healthy. I can’t control what they are going to do with me,’’ Wheeler said, facing the reality of the situation. “I’ve got to show them I can pitch. I’ve got to show them I can get outs. I’m just focused on being healthy and pitching.’’

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Steven Matz’s locker is right next to Wheeler’s at the far end of the Mets clubhouse – Aces Row.

“I’m real excited for him,’’ said Matz, who underwent Tommy John surgery in 2010 as a minor leaguer. “I’ve been there and done that. For him, he’s been in the big leagues, and he knows what kind of success he’s had. He got to see us go to the World Series, watching on the sidelines, that must have been really tough. He’s been working really hard, sticking to it, and it’s just great to see him back.’’

Wheeler has learned so much in the past year about himself. He is not going to allow himself to get too excited about his return because last year’s setbacks were so crushing.

“Last year I had my hopes up. This year I am just going start by start,’’ the right-handler said. “Even just bullpen session by bullpen session. So it’s a little different than last year. This year I am a little more laid back, I guess.’’

The original game plan was to return around the All-Star Game last July. All that went out the window, and he has become the Shadow Pitcher.

Everything is day to day with Wheeler. There are no big plans. Only a big sigh of relief when another test is passed.