WASHINGTON — The Washington Nationals signed Jayson Werth to show them how to win.

His game-ending home run Thursday night extended their surprising season.

Werth led off the bottom of the ninth inning by driving Lance Lynn’s 13th pitch into the left-field stands to give the Nationals a 2-1 victory over the defending World Series champion St. Louis Cardinals and force a Game 5 in their National League division series.

As he circled the bases, Werth raised his right index finger in a “No. 1” gesture while the announced crowd of 44,392 roared. The other Nationals raced out of the dugout to greet Werth, who tossed his red batting helmet high in the air before jumping on home plate and being enveloped by bouncing teammates.

The best-of-5 series will end tonight in Washington, with the winner advancing to face the San Francisco Giants in the NL Championship Series. The starters will provide a rematch of Game 1, which Washington won, with Gio Gonzalez on the mound for the Nationals and Adam Wainwright for the Cardinals.

“It’s what it’s all about,” Werth said. “It’s what you play all season for and what you work out all winter for and what you get to spring training early for. We have a chance tomorrow to take that next step. I know my teammates will be ready and the city will, too.”

The home run was Werth’s first in the postseason with the Nationals but the 14th of his career. He won the 2008 World Series and a string of division titles with the Philadelphia Phillies before moving to Washington as a free agent before last season on a $126 million contract that stunned much of baseball.

He gets a ton of credit for helping steer a quick turnaround. The Nationals lost 100 games in 2008 and 2009 but led the majors with 98 victories and won their division this year.

“When I signed here, my first day here, I went to a Capitals game, a hockey game, the place was packed. Somebody said, ‘Just a few short years ago, this place was empty,’ ” Werth said. “So I knew that a winning ball club would bring the fans, and here we are, two years later, and they’re showing up and it’s awesome.”

Werth’s shot provided a sudden end to a classic postseason contest filled with tremendous pitching. Each team managed only three hits.

Lynn, usually a starter for St. Louis but a reliever in these playoffs, was making his third appearance of this series. He was the Cardinals’ third pitcher - and faced only one batter - and Manager Mike Matheny was asked afterward why he didn’t use closer Jason Motte.

“If we were at home, it would have been a very easy decision to bring in Motte,” Matheny said, explaining that if he used up his closer and St. Louis went ahead later in the game, a reliever not used to getting a save would have needed to try. “Had a lot of confidence in Lance. He came in throwing the ball well. Werth just put together a very good at-bat.”

Cardinals batters did not have good at-bats down the stretch. They struck out eight consecutive times against three Nationals pitchers - Jordan Zimmermann, Tyler Clippard and Drew Storen, who threw the top of the ninth and got the victory.

Storen walked No. 8 hitter Pete Kozma with two outs in the ninth before getting pinch-hitter Matt Carpenter out on a twisting, stumbling overhead catch by shortstop Ian Desmond, who wound up sliding on his belly in short left field. When Desmond rose, he threw the ball into the stands and yelled.

Moments later, Werth had all the red-clad, towel-twirling spectators yelling, too, thanks to the way he turned on a 96-mph fastball. For much of the game, the hometown fans were rather quiet, perhaps dreading a sooner-than-expected end to their team’s better-than-expected year.

Starters Kyle Lohse, who won the wild-card playoff game for St. Louis against Atlanta last week, and Ross Detwiler were both superb.

Lohse lasted 7 innings, allowing 1 run and 2 hits. Detwiler went 6 innings, and gave up 1 unearned run and 3 hits.

Lohse was replaced by Mitchell Boggs, who struck out pinch-hitter Chad Tracy with a man on to end the eighth, before giving way to Lynn.

While the young Nationals are new to this sort of thing, the wild-card Cardinals have quite the postseason pedigree: Over the past two years, St. Louis is 5-0 in games where it faced elimination, including victories in Games 6 and 7 of the 2011 World Series against the Texas Rangers.

“We got a lot of experience, a lot of confidence built. Just going to the World Series and winning the World Series, having to play a Game 7 and come out on top - you’re seeing a lot of us use that experience so far in this post season,” St. Louis first baseman Allen Craig said. “We had a tough, do-or die game in Atlanta and came out on top, and after we won that game I think we started to feel really good about ourselves and get that feeling like we had last year.”

Sports, Pages 17 on 10/12/2012