It was the home run that healed New York. Baseball Hall of Famer Mike Piazza, 53, tells The Post’s Dean Balsamini about his emotions on the evening of Sept. 21, 2001, at Shea Stadium. The Mets were losing to the rival Atlanta Braves 2-1 when Piazza’s dramatic, two-run, eighth-inning homer propelled the team to victory — and lifted the spirits of heartbroken New Yorkers.

It doesn’t seem like 20 years. I can’t believe it. Part of our recovery is to suppress certain feelings and emotions. You recall, but as life moves on, you build up scar tissue. Now that the 20-year mark is coming around, those old feelings come to the forefront.

I paid attention to everything that night. The bagpipes for me were the biggest challenge. It’s such a powerful instrument. I don’t see how you couldn’t have been affected.

The NYPD helmet I wore for the game came together organically. We were just trying to do what we could to honor the first responders. You gotta give a lot of credit to our equipment guy, Charlie [Samuels]. Because I wore the catcher’s helmet, Charlie had to cut out the letters and paste them on, glue them on. We were a little defiant about it. [It was against MLB rules to wear anything but a team logo.] We felt very strongly about it. We felt it was the right thing to do. We didn’t want anybody telling us, ‘No.’ We said, ‘If there’s a fine, we’ll pay the fine. We don’t care.’

As for playing that night, we had to dig down deep to find focus. Baseball is a very difficult game to play under normal circumstances. Under extraordinary circumstances, it’s that much more difficult. I felt the support. I felt the people pulling for us. It was palpable. It’s something that engulfs you and inspires you.

How did I feel during the game? A lot of fear. A lot of prayer. I didn’t think I would be able to get through the night emotionally. I just wanted to survive — metaphorically, of course. I felt those feelings coming out of me. That emotional distress, like being at a funeral or seeing someone suffering. It does pull at you. It takes energy from you. And then you have to go out and execute as an athlete on the highest of stages.

For me, it was nothing short of divine inspiration. For that one moment — the home run — I felt an extreme sense of calm. Maybe that was the gift I had as an athlete. The ability to focus. The ability to block everything out and slow the moment down. I do remember that very vividly, saying, ‘OK, it’s a big moment here. Calm down. Get a good pitch to hit. Put a good swing on it. Don’t try to do too much.’

I thought I hit it pretty well. It was a good feeling. I felt the energy and I felt the cheering. Once I crossed home plate I knew — like, this is pretty cool. And people were going nuts. When I came out for the curtain call, I looked up to just thank and dedicate it to those we lost. That was on my mind.

The home run will always be with me. It’s on my Hall of Fame plaque. The way I perceived it? A feeling of gratefulness — that I was able to be in the right place at the right time and able to come through.

I’ve always shied away from people calling me a hero. We provide inspiration, entertainment and a way for people to join together as family and friends — but obviously it’s not life or death. It’s an honor that it brought people a little bit of joy.

The people who lost their lives — not only the victims but the first responders that ran in to save people — is what we are about as a people, as a country. We are about an idea, brotherhood, and love and family. It’s wonderful to see the legacy of these first responders is not forgotten.

People ask if the country can ever get back to the unity we had post-9/11. I hope so. For that one period of time, we saw more of what we have in common instead of our differences. I don’t think anyone really cared about politics. We all just cared about each other.

I don’t know of anybody who wasn’t changed by 9/11. I realize how fragile life is. We always take it for granted. Life is fragile and precious and can be snatched at any moment.

When I walk the city now I do find a lot of people want to talk about the home run. It’s part of the continued process of healing and people want to relate to it and I enjoy it. Every now and then someone sees me in an airport and comes up and wants to talk about it. I’m always there. I listen. It’s an honor for me. I feel a responsibility to try to just continue to console them.