Gary and Robin Rosenthal made one last detour on their way out of Nationals Park on Tuesday night, peering over the railing of the gallery level along the third base line and onto the field, where the Washington Nationals were celebrating their first National League pennant.

The married couple of 35 years shook their heads in disbelief as fans around them snapped photos and took videos of the scene below, just in case they needed proof in the morning that the Nationals’ 7-4 win to complete a sweep of the St. Louis Cardinals in the NLCS really happened.

“I was thrilled to death when the Nationals showed up in 2005,” said Gary Rosenthal, who turned 63 on Wednesday and received tickets to Game 4 as an early birthday present from his wife. “I grew up with the Senators. This may be my biggest sports memory, topping anything Redskins, Wizards or Capitals. We haven’t had a World Series here since 1933, and I’ve always been more of a baseball fan.”

“It’s unbelievable,” said season plan holder Liz Pomper, who has attended every playoff game at Nationals Park and therefore been subjected to her fair share of postseason heartbreak. “This is the moment we’ve been waiting for.”

It took roughly 20 minutes for the idea of Washington’s baseball team advancing to the World Series for the first time in 86 years to go from believable to seemingly inevitable. In the span of four outs to open the game, Nationals pitcher Patrick Corbin struck out the side and Ryan Zimmerman crossed the plate with Washington’s fifth run.

Given how Corbin was pitching and how the Cardinals’ offense, which somehow managed to score 10 runs in one inning against the Atlanta Braves last week, had looked in this series, five runs would be plenty. When Washington took a 7-0 lead on a Trea Turner single before the first inning was over, the only question was how the rocking home crowd of nearly 44,000 could maintain its energy level for another 24 outs.

“I was a little nervous when we were up [7-0],” said Pomper, who wore a “Baby Shark” hat and couldn’t help but recall the horrors of Game 5 of the 2012 NLDS, when the Nationals blew an early six-run lead against the Cardinals.

“I thought a lot of us were kind of bored after the first inning,” Nationals fan Sandeep Taxali said. “We thought, ‘Okay, this is going to be slow. We’ll win it and we’ll celebrate, but there’s not much of a game here.’ Then the tide starting turning, and the nerves started popping.”

The Nationals’ bats went silent. Yadier Molina hit a solo home run in the fourth, and the Cardinals added three more runs off Corbin in the fifth, cutting Washington’s lead to 7-4. In the unusual position for a second straight game of taking a big early lead and then trying to keep its opponent from getting up off the mat, the “Stay in the Fight” Nationals absorbed a few blows that left them wobbly and some of their fans mildly concerned.

“I chewed on my [rally] towel a little bit,” Gary Rosenthal said. “I kept thinking, ‘Where did the hitting go? What are we doing?’ ”

“Ninety-nine percent of the games we’ve been to this year have had drama, so we weren’t surprised,” Nationals fan Frankie Engelking said. “It was like the whole season. It was up and down, ‘We’re going to make it, no we’re not,’ but we never gave up."

There was a jolt of energy in the sixth, when Gerardo Parra stepped to the plate as a pinch hitter for the first time in the series, resulting in the largest — and perhaps loudest — “Baby Shark” singalong in Nationals Park history. Parra singled to right, prompting another round of singing and hand-chomping, before Turner struck out to end the inning.

St. Louis went quietly in the seventh, but the Cardinals mounted another rally in the eighth, loading the bases against Sean Doolittle and Daniel Hudson. By then, the crowd was fully engaged again, roaring or groaning after every pitch.

“Three! More! Outs!” 27-year-old Nick McMillan, who wore a Senators jersey, shouted to no one in particular after Hudson got Matt Carpenter to ground out to end the threat. McMillan then belted out the words to the Beastie Boys anthem “Fight For Your Right,” which blared over the ballpark’s speakers during the half-inning break.

When Victor Robles squeezed Tommy Edman’s flyball to center field for the final out of the game, it set off a celebration in and around the ballpark as fireworks lit up the sky. Fans twirled their red rally towels and hugged and high-fived each other and Nationals Park ushers amid isolated showers of beer and popcorn.

“I am so happy, I’m dancing,” said Dan Smith, who also high-fived and hugged the people he has gotten to know in the seats near his standing-room spot beneath the press box in Section 313. “I remember standing here in early May and saying, ‘The math says we can’t make the playoffs.’ I’ve never been more happy to have been wrong.”

Just after midnight, two gentlemen who will remain anonymous lifted up their T-shirts and bumped bellies on the left field concourse because what better way to celebrate a World Series berth?

“Come on, who knows when this will happen again?” one of them asked rhetorically, to which the appropriate response is, “Hopefully within the next 86 years.”

“This ameliorates everything,” original season ticket holder Marlene Koenig said of the Nationals’ playoff history, which included four defeats in four trips to the NLDS before this year. “We’ve conquered all the demons. … You have to invest in a team, win or lose. You can’t just be there for the highlights. You learn about life, and you learn about grief. You have to go through the highs and the lows. This was such a surprise, with the wild card and beating the Dodgers, it’s been surreal.”

Koenig added: “Everyone can chill out and get drunk tonight, for what, the fourth time in three weeks?"

With six days off before the start of the World Series, there’s plenty of time to soak in this latest moment.

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