Shelby Miller earned his 15th win with relief help from Seth Maness, Kevin Siegrist, Carlos Martinez and Trevor Rosenthal in a 4-1 victory that spoiled Jordan Zimmermann's bid for his 20th win and wrapped up a three-game sweep on Wednesday.
All are 24 or younger, and all have been filling critical roles for a while now.
"We know what's at stake and what we need to do to get the job done, how many games we need to win," Miller said. "Hopefully, we can just win them all.
"It's just been an amazing year, I've had so much fun and there's still a lot of baseball left."
Miller (15-9) has been in the rotation all year and leads major-league rookies in wins after allowing a run in six-plus innings. Maness induced a double-play ball in the seventh, Siegrist hasn't allowed a run in an NL-best 23 1/3 scoreless innings and has a microscopic 0.47 ERA and the 23-year-old Rosenthal saved all three games in the series.
"It's been a fun year, especially right now," Rosenthal said. "Guys are getting to pitch in different situations than they had all year. Everybody's stepping up."
Yadier Molina had the go-ahead hit and Matt Adams homered for the Cardinals, seeking their first division title since 2009. Manager Mike Matheny reported screaming in the clubhouse after the Cubs' Darnell McDonald's go-ahead three-run homer off Francisco Liriano in a 4-2 victory over the Pirates and admitted he'd taken peeks at the scoreboard.
"Yeah, I was guilty again of watching during the game," Matheny said. "It wasn't my intent, but it did happen."
Molina had an RBI in all three games for the Cardinals, who swept the season series 6-0.
Zimmermann (19-9) allowed four runs in seven innings. The Nationals had five hits one day after breaking up rookie Michael Wacha's bid for a no-hitter in the ninth inning.
"I'm not really disappointed," Zimmermann said. "Twenty wins is a lot of wins and 19 is not too far off."
Adams hit his eighth home run since replacing injured Allen Craig earlier this month and doubled for the Cardinals, who lead the Pirates by three games with three to go. The Reds lost 1-0 to the Mets on Wednesday and were eliminated from the divisional race.
The Cardinals (94-65) are a season-high 29 games above .500 and have a day off before 14-game winner Lance Lynn faces the Cubs on Friday night to open the final series.
Miller was wild high early and walked two of the first three hitters to set up Bryce Harper's RBI single. The Nationals had no other runners in scoring position against the 22-year-old Miller, who allowed a run in six-plus innings and beat them for the second time this season.
Miller was 10-3 with a 1.75 ERA at home, becoming the third pitcher to reach double-digit victories at eight-year-old Busch Stadium.
"I didn't think he had too much," Nationals manager Davey Johnson said. "I thought he was all over the place and really wasn't setting up his pitches and we helped him out in a lot of situations."
Zimmermann had won his previous four appearances and had been coming off a two-hit shutout of Miami. But he is 0-3 with an 8.27 ERA in six career starts against St. Louis, and lost Game 2 of the NL division series last fall.
Daniel Descalso doubled leading off the third and scored on Matt Carpenter's groundout to tie it. Zimmermann hit Matt Holliday to open the fourth, and Adams doubled ahead of Molina's two-run single that made it 3-1.
The Cardinals were 15-2 against the NL East and also swept Miami and Philadelphia.
Zimmermann has 43 career wins, one shy of the Nationals' franchise record held by Livan Hernandez. ... Miller's 15 wins is the most by a Cardinals rookie since Dick Hughes won 16 in 1967. ... Lynn (14-10, 4.09) faces Travis Wood (9-11, 2.98) on Friday. Stephen Strasburg (7-9, 3.02) gets his final start on Friday at Arizona against Patrick Corbin (14-7, 3.28). ... Jon Jay has 16 hits and is batting .340 during an 11-game hitting streak.