Joy lived Thursday evening in the chill at Nationals Park, the unbridled kind, completely focused on the moment. Jayson Werth provided it with a laser of a home run in the bottom of the ninth, a blast over the left field wall that gave the Washington Nationals a mesmerizing 2-1 victory over the St. Louis Cardinals. Instantly, a full day of worry and hours of hair-pulling tension were replaced by euphoria, the District’s best baseball moment in generations.

But those thoughts, that jubilation and Werth’s helmet-tossing trip around the bases merely delayed the reality that this all happens again, and then some, Friday night. Werth’s homer set up another day of the season, another day to expand ulcers and shorten fingernails for the 44,392 fans who filled the park — and well beyond.

“It’s the finality of it,” said Nationals General Manager Mike Rizzo, the architect of this club. “One of two really good baseball teams is going to go home, and their season will be over.”

It is set then: A no-room-for-error, win-or-grab-the-golf-clubs matchup at 8:37 p.m. Friday at Nationals Park. It will be the fifth game of this National League Division Series, with the winner advancing to play the San Francisco Giants in the National League Championship Series. It will be the Nationals’ 167th game of this season. It will be the 1,299th Nationals game since baseball returned to Washington, back in 2005. And it will be unlike any other the town has seen.

“This is what it’s all about,” Werth said. “This is what you play all season for. This is why you work out all winter. This is why you start playing tee-ball when you’re 4.”

Without Werth’s home run, after a battle of an at-bat with Cardinals reliever Lance Lynn, there might be none of this anticipation. In this best-of-five series, the Nationals entered Thursday’s game trailing two-games-to-one, facing elimination already. With his swing, Werth wiped out losses in Games 2 and 3 in which the Nationals had been outscored 20-4, and provided so much — another day to looking forward, but a moment, too, on which to look back.

“It establishes us as a baseball town,” said Mark Lerner, one of the team’s owners. “I think it’s a moment people will talk about 50 years from now.”

But will it extend the season by a day or a week? Only Friday will determine that. This is a conversation topic District baseball fans — a group that endured losing ballclubs for decades, only to have the team ripped away not once, but twice — haven’t chewed on for the better part of nine decades. Both the fans and the players are only in the process of learning what enduring the postseason is like.

“These games, they’re exhausting,” third baseman Ryan Zimmerman said.

So prepare to get worn out again.

In 1924, the old Washington Senators trailed the New York Giants by two runs in the eighth inning of Game 7 of the World Series. Bucky Harris, the second baseman, hit what looked like it would be a routine groundball toward third base. The ball, though, hit a pebble on Griffith Stadium’s infield. Because this happened in one of these decisive games, the pebble now has legendary status. The ball bounced over the head of the Giants third baseman and into left field. Two runs scored, star pitcher Walter Johnson came on in relief, and the Senators won in the 12th on another bad-hop ball toward third, this one hit by Earl McNeely, scoring Muddy Ruel — legends, both, because of their involvement in that elimination game.

The next year, Washington faced Game 7 of the World Series in Pittsburgh. Yes, hockey’s Capitals have played six decisive games — all in best-of-seven series — over the past five seasons. A generation ago, basketball’s Bullets (now the Wizards) won the city’s only championship in that sport by beating Seattle in Game 7 of the 1978 NBA Finals. But this will be Washington’s first all-or-nothing baseball game since the 1925 Senators couldn’t hold an eighth-inning lead and fell to the Pirates.

Friday’s Game 5 comes two rounds before the World Series. But it is, in essence, the reason the Nationals have played those 166 previous games, over which they have the best record in the sport.

“We’ve worked extremely hard to get home field advantage for the playoffs,” Rizzo said. “It’s come to fruition that we get home field advantage in Game 5, an elimination game.”

For that game, the Nationals will hand the ball to pitcher Gio Gonzalez, the perma-smiling left-hander who won 21 games during the regular season and is a strong candidate to win the Cy Young Award as the National League’s best pitcher. “It’s still loose in the clubhouse,” Gonzalez said before Game 4, even as the Nationals faced elimination. It is exactly how the Nationals expect Gonzalez to approach his task Friday, with the season again in the balance.

“I’ve never seen a happier person in my life, any time of the day,” Zimmerman said.

That is the sense that pulsed through the home clubhouse. There is, at least, one more game to play. Be happy about it.

“We’ve got a chance to win the series tomorrow,” Werth said. “What a difference a day makes.”

Werth smiled through his beard. He has endured these moments, back when he played on contending teams in Philadelphia. Most of the Nats have not. What to expect?

“You have no idea,” closer Drew Storen said. “You just go into it, and you don’t really think about it.”

So try not thinking about it, Washington, over the endless hours before Gonzalez fires that first pitch. The season will either live Friday night, or it will die. There will be joy or there will be doom. And for the first time in nearly 90 years, this city will have to deal with it, one way or the other.