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 with delight. 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 homer was Werth's first with the Nationals but 14th of his career in the postseason. 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 wins and won their division this year.
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 wild-card Cardinals' third pitcher -- and faced only one batter.
Storen walked No. 8 hitter Pete Kozma, 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.
Link to boxscore: Washington 2, St. Louis 1