WASHINGTON — The Washington Nationals signed Jayson Werth to show them how to win. His game-ending homer 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 NL 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 a bouncing collection of thrilled teammates.

The best-of-five series will end Friday night 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 will be a lot like today. It's what it's all about. 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," Werth said. "We have a chance tomorrow to take that next step. I know my teammates will be ready and the city will, too."

The homer 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.

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. "Had a lot of confidence in Lance. He came in throwing the ball well. Werth just put together a very good at-bat."

No outs when winning run scored. E — Desmond (1). LOB — St. Louis 8, Washington 2. HR — LaRoche (2), off Lohse; Werth (1), off Lynn. RBI — Beltran (4), Werth (1), LaRoche (2). S — Lohse. SF — Beltran. Runners left in scoring position — St. Louis 2 (Holliday, Descalso). RISP — St. Louis 0 for 3; Washington 0 for 0. Runners moved up — Y.Molina. GIDP — Morse. DP — St. Louis 1.

Pitches — Lohse 87, Boggs 14, Lynn 13, Detwiler 104, Zimmermann 12, Clippard 16, Storen 26. Lynn pitched to 1 batter in the 9th. IBB — off Detwiler (Freese). Umpires — Home, Jim Joyce; First, Alfonso Marquez; Second, Ed Hickox; Third, Paul Emmel; Right, Joe West; Left, Marvin Hudson. T — 2:55. A — 44,392.