The Nationals dugout and Nationals fans watch the 18th inning as the Nationals lose to the Giants 2-1 in the second game of the National League Division Series. (Toni L. Sandys/The Washington Post)

For eight-and-a-half innings, it was all about the win. Then, suddenly, it was all about the wind.

The red-garbed mob at Nationals Park believed their Nats would win Game 2 against the San Francisco Giants on Saturday night and tie up the National League Division Series at a game apiece.

But then weather gods and baseball gods alike changed their fickle minds about the fate of the happy throng below. With only one out to go, a one-run lead was lost, the bracing fall wind became a biting winter gale and the joyful outing morphed into a grueling 18-inning slog. The six-hour, 23-minute marathon, the longest game in postseason baseball history, delivered a bitter ending.

“I feel like I’ve been hit by a truck,” said Stewart Vandiver as he shuffled out of the center-field gates just after midnight after the 2-1 loss to the Giants. “An ice truck.”

Like many, Vandiver had a white rally towel, which he had been cheerfully waving during the happier half of the evening, now wrapped around his neck as a makeshift scarf.

With temperatures in the 40s and a stiff wind blowing, some freezing fans had the rally towels stuffed in their summer-weight jerseys, the “Harpers” and “Zimmermans” on the backs bulging with the odd padding. Clots of frigid refugees huddled around TVs in the concourse, behind pillars, in the bathrooms, as their once-scorching team flailed helplessly inning after inning in the sudden winter gloom.

Vendors on the 100 level restarted their deep fryers to provide french fries to the shivering masses. The lines for hot chocolate were yards long.

Kathy Gutierrez, 65, who lives in Bowie, was wringing her hands inside her newly bought hoodie, which she snagged before the park’s stores sold out of them.

Thousands of other Nats partisans headed for the exits, an exodus derided by sports pundits and hard-core baseball fans on Twitter.

Those who stayed to the very end were reeling afterward. How had the wonderful season become a postseason nightmare so quickly?

Saturday’s game was a yin-and-yang doubleheader. The first nine innings, though close, were a continuation of the winning ways fans had come to expect from their National League-leading squad. But after the Nats let the Giants catch up, the second nine innings were the beginning of a painful purgatory.

What if manager Matt Williams hadn’t replaced the shutout-pitching phenom Jordan Zimmermann with snake-bitten closer Drew Storen with one out to go? That’s the question that will linger for a baseball eternity if the Nats don’t pull off a long-shot comeback from two games down now that the series has moved to San Francisco. They need to win three games in a row to do it.

The Washington Nationals lost a second game to the San Francisco Giants in the longest post season game in MLB history. Jordan Zimmermann, Drew Storen, Bryce Harper, Asdrubal Cabrera and Tyler Clippard share their thoughts on what went wrong and why the next game is important. (Whitney Leaming/The Washington Post)

“We’ll never know what would have happened if he’d left him in,” said Molly Galvin of Takoma Park, who spent a few minutes of every inning thawing in the women’s room with like-minded refugees. “It’s just incredibly, incredibly disappointing.”

Galvin and other die-hards had come in hopes of purging the memories of the Nats’ last playoff appearance and left feeling as if they’d been trapped in a rescreening of the same horror flick. The final inning, the brink of glory, the same pitcher, the plunge into the slough of despair.

“In Yogi’s words, I hope it’s not deja vu all over again,” said Garland Cooper, 68, of Lovettsville, Va., who was present That Night two years ago. “Just check me into the hospital right now and keep the sharp objects from me.”

The evening started with promise for the sellout crowd of 44,035. Zimmermann, hot off his no-hitter on the final game of the regular season, kept spirits warm by retiring one batter after the other. Some fans were feeling the stress of having only one run for a cushion.

“We are a little stressed but are hoping for the best,” said Will Slaughter of Alexandria. His wife, Carter, said he watches so many games at home that she hasn’t been able to watch television for months. They groaned at the mention of the 2012 game that ended the Nationals’ playoff run. “We’re trying to deal with everything positively.”

Then the ruinous ninth. Fans who had been gathering their things for a winning march to parking lots and Metro stations stared in disbelief as the tying run came home on Pablo Sandoval’s double. The hit let the air out of the crowd and let in the chill that glee alone had held at bay. The fate of not just the game, but the season seemed suddenly in the balance.

“If they don’t win the game, we lose the series,” predicted Karl Lady, who lives in Alexandria. “If we win this game, we’ll win the series.”

Lady, 73, had seats in the upper deck with his friend Steve Winchell. After the 12th inning, they had to flee the chill. They sheltered behind a wall on the clubhouse level, listening to the radio play-by-play echoing through the stadium. Finally, he made a dash for home and warmth and television. That’s where he saw inning after inning of death-struggle bullpen pitching with the score locked at one each. That’s where he saw Giant Brandon Belt finally break through, hitting a go-ahead home run in the 18th.

“It was awful,” the retired businessman said. “They can recover, but will they recover? The chances are not good.”

Lady, a lifelong Cubs fan, knows something about losing. But the Nationals “stole a piece of his baseball heart” when they came to Washington. After years of practice, Lady has learned that in baseball — and life, for that matter — the opportunity for success comes with hope.

“I have that eternal optimism,” he said.

Now Nats fans have reverted to form, switching from hoping to coping.

“It isn’t over,” said Elizabeth Ortiz, 27, an office manager from Sterling. “They’ve come back before. They’ve been on amazing road trips this year.”

Her friend, Cori Grillo, 32, a hairstylist from Springfield, said she got chills when she walked into the park Saturday. The good kind. Hours later, she was just cold, barely protected from the wind by her Nats pajama pants, identical to her friend’s.

They also shared a just-happy-to-get-this-far fatalism of the oft-disappointed fan.

“In football, I root for the Buffalo Bills,” said Grillo, a New York native. “I’m used to losing. To me, just to make the playoffs is exciting.”

Ortiz shrugged. “I’m a Skins fan,” she said. “Same thing.”