Rookie Tyler Moore delivered a pinch-hit, two-run single in the eighth inning to turn a 2-1 deficit into the game-winning margin of victory for the Nationals, whose 98 wins this season led the major leagues and made them top seed in the playoffs.

"He threw me some pretty tough pitches and I managed to foul them off," Moore said about his at-bat against lefty reliever Rzepczynski. "So I just thought I'll stick (the bat) out there, put the barrel on one and it flared into right field."

The Cardinals, who beat the Atlanta Braves on Friday in a one-game wildcard showdown to advance to the division series, squandered a bases-loaded no-out opportunity in the bottom of the seventh inning by failing to score.

That turnaround of fortune was the key to a game in which the Nationals scored one run in the second and the Cardinals answered with two runs without benefit of a hit in their half of that inning for all the runs they would muster in the game.

In the seventh, Jon Jay led off by reaching first base on an error by first baseman Adam LaRoche, Carlos Beltran singled to center and reliever Craig Stammen hit Matt Holliday with a pitch to load the bases.

Nationals manager Davey Johnson summoned Ryan Mattheus to take the mound.

"I said to him we need a couple of ground balls to get out of this inning and he did it," Johnson said.

Mattheus wasted no time obeying his manager's orders, using two pitches to register three outs.

Clean-up hitter Allen Craig, who had led the National League in batting with runners in scoring position, bounced to short on the first pitch and Ian Desmond fired home to get the lead runner.

On his next pitch, Yadier Molina grounded to third base where Ryan Zimmerman started a double play that ended the threat.

'HOSTILE ENVIRONMENT'

In the eighth, with St. Louis reliever Mitchell Boggs on the mound, Michael Morse reached on an error by shortstop Pete Kozma to begin the game-winning rally

Desmond, who had three hits in the game, followed with a single to right to put men on first and third. A sacrifice bunt gave Washington runners on second and third and after Kurt Suzuki struck out, left-hander Rzepczynski was brought in.

That set the stage for rookie Moore.

"Just coming into a hostile environment like this, tried to settle my nerves down and put the ball in play as best as I could," said Moore, who poked a soft single to right that was good enough to score both baserunners and send the Nationals on their way to victory.

Tyler Clippard pitched the eighth and Drew Storen set the Cardinals down in order in the ninth to finish it.

St. Louis managed just three hits in the game, taking advantage of the wildness of Washington starter Gio Gonzalez to score a pair of runs in the second. Gonzalez, a 21-game winner, walked seven batters in the game.

Cardinals slugger Matt Holliday said the shadows that fell across the diamond made it hard to identify the pitches.

"It's hard to hit when you can't see the spin on the ball," Holliday said.

Manager Mike Matheny said it was the same for both clubs and that his Cardinals players should not be making excuses. "Once you start going on that road, you're on the trail to fail. You just got to make adjustments."

St Louis starter Adam Wainwright was a hard-luck loser, dazzling the Nats with his curveball, striking out 10 batters in five and two-thirds innings and yielding one run.

The best-of-five series resumes on Monday in St. Louis.

(Reporting by Larry Fine in New York; Editing by Frank Pingue)