WASHINGTON — The quartet sat there, afraid to move in the Washington Nationals’ clubhouse, while the father sat in the stands Saturday night at Nationals Park, his heart pounding against his chest.

Ron Harper has seen his son in these moments through his entire life, whether he was 10 years old playing in a travel ball championship tournament, playing in the Pan Am Games as a teenager, pitching against Cuba, playing in the Junior College World Series, or stepping up in the eighth inning with the Nationals’ season on the line.

“I believe he’s built for that moment,’’ Ron Harper said in the aftermath of the Nats’ 6-3 victory in Game 2 of the Division Series over the Chicago Cubs. “That’s being confident in yourself more than anything. You just make the most of that moment, and it just so happens to be on this type of stage.’’

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The Nationals, who had already lost the first game of the best-of-five series, were losing again to the Cubs, 3-1, and down to their final five outs before their season became all but extinct.

Harper, who missed nearly two months before returning the final week of the season with a bone bruise and calf strain, stepped to the plate with one out and pinch-runner Victor Robles at first base. He swung and badly missed at Cubs reliever Carl Edwards’ first-pitch curveball, with the sellout crowd groaning. Harper then watched Edwards throw three fastballs in a row, none in the strike zone, falling behind 3-and-1.

 “I didn’t think he was going to throw a pitch over the plate,’’ Harper said, “to tell you the truth. I thought he was going to throw a curveball back down in the dirt. I thought about taking the whole way.

“And then I saw the loop in the curveball, and said, ‘Why not swing as hard as you can?’ ’’

And he connected, sending the pitch screaming into the night, landing into the upper deck.

“Pretty good moment,’’ Harper said.

Just like that, the game was tied, and 14 pitches later, it was over, with Ryan Zimmerman hitting a three-run homer, tying the NL Division Series at one-apiece as the two teams head to Wrigley Field in Chicago.

It was instant bedlam, with Ron Harper hugging his wife, telling her he loved her. Reliever Brandon Kintzler fist-bumped closer Sean Doolittle and then screamed in his face. The boys in the Nats clubhouse jumped up, ran around, and acted like they were 12-year-olds in Little League.

“It was like a volcano erupting,’’ Game 2 starter Gio Gonzalez said. “You had everybody in here running around. You could just hear the rumble from the stands in here.’’

It was the hit that saved their season, the hit that showed the world that Harper is back from his injury, and the hit that may prove to be the biggest one in the franchise’s history.

So why should anyone be surprised that it was Harper, the Nats’ biggest star, the one who will be paid at least $400 million, or maybe even $500 million in a year, who delivered the hit heard clear to the White House?

“I don’t know if he’s supposed to do it,’’ says Ron Harper, a Las Vegas iron worker whose physique makes him look nearly as young as his son, “but he just doesn’t shy away from it.’’

Considering this moment, and what was at stake, just where does this possibly rank in the 24-year, 356-day life of Harper?

“I’ve got to search back,’’ Ron Harper says. “I’ve seen him do some special things since he was 12 years old that I’ll never forget in my life.’’

The kind of stuff that lands you on the cover of Sports Illustrated at 16.

“That was a long time ago,’’ Ron Harper says, laughing.

 “He’s always been known for hitting home runs, and hitting them far,’’ says Cubs third baseman Kris Bryant, who grew up in Las Vegas with him. “You just can’t make a mistake to him. He’s a really good hitter, and so young, and super-smart.’’

And, oh, so talented.

“I’ve really been in awe of Bryce having a flair for the dramatic,’’ Doolittle says. “Even though there’s these expectations for him, and this inherent pressure for him to live up to these monumental things that that people expect him to do, he constantly lives up to them.

“And he’s handled it with a lot of class.’’

When the game ended, and everyone retreated to the Nationals clubhouse, there was Harper standing in the corridor, huddled with his wife and family, holding his sister’s baby, posing for family pictures.

He finally needed to go back into the Nats’ clubhouse, get dressed, and head to a press conference, but not before hugging his dad one last time, and telling him, “I love you.’’

The Nationals have never won a postseason series, but instead of a burden, they feel momentum. The mojo. And yes, even the superstitions.

While everyone was admiring the heroic feats of Harper and Zimmerman, it was the gang in the clubhouse, those who refused to shift seats, who believe they were responsible for that good karma.

When the inning started, injured pitcher Joe Ross came into the clubhouse to grab a cup of coffee. Pinch-hitter Adam Lind, who had played 1,344 games before reaching the postseason, started it off with a leadoff single. They told Ross to sit down, and refused to let him retreat back to the dugout. So there they were, Gonzalez, relievers Matt Albers and Sammy Solis, all sitting alongside one another for good luck.

 “You didn’t want to move,’’ Gonzalez said. “You didn’t want to say anything. You didn’t want to change what you were doing.’’

Said Albers: “It was fun, man. I felt like a little kid watching the game. And as soon as Bryce hit that, we were going crazy in here.”

When it was all over, the boisterous crowd erupted a final time, and the clubhouse filled with euphoria, they promised to have the same ritual in Chicago.

It’s sure to work, they boldly predict, as long as a certain right fielder with long brown hair and a thick beard, keeps working his own magic.

“D.C. is great, isn’t it?” Ron Harper says. “They’re starting to become baseball fans. They’ve been football fans and Caps’ fans forever. They’re starting to catch on that we’re pretty good.’’

And embracing a right fielder whose thunderbolt in the sky woke up an entire team, and made this a playoff series, perhaps one this city will never forget.

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