St. Louis scored often and early to keep some distance in the wild card chase with a 12-2 victory over Washington in the opener of a three-game set.
With five games to go, the Cardinals now hold a three-game lead over the Los Angeles Dodgers for the final wild card spot in the National League.
Allen Craig went 4-for-4 with two RBI and two runs scored while Yadier Molina and Shane Robinson each hit a solo home run for the Cardinals, who have won five of six.
"We have to take things one game at a time and not get ahead of ourselves," said Craig. "We need to just focus on playing good baseball and get into the playoffs."
Adam Wainwright (14-13) was the beneficiary of some early run support and pitched well himself, giving up just one run on five hits over six innings to win for the first time since Aug. 26. He went 0-3 in his previous five starts.
Roger Bernadina hit a solo home run and Adam LaRoche drove in the other run for the Nationals, who had won their previous two. Edwin Jackson (9-11) was lit up for nine runs -- eight earned -- on seven hits in just 1 1/3 innings.
Washington is now tied with Cincinnati for the best record in the majors. Cincinnati got a no-hitter from Homer Bailey in a 1-0 win against Pittsburgh on Friday. The team still holds a four-game lead over Atlanta for first place in the NL East as Atlanta lost to the Mets on Friday.
"It's getting down to the wire and we know that," said Jackson. "We like our chances, but nothing is done until it's sealed up so we're just staying positive and will keep playing hard."
Washington struck in the first inning when Bryce Harper doubled and later scored on an LaRoche single, but it was a short-lived lead.
The Cardinals put their first three runners on in the bottom half to load the bases and tied the game on Craig's RBI single. Molina then reached base on an error by Ryan Zimmerman, scoring one more run and Carlos Beltran followed with a walk to bring in another. Following a Daniel Descalso sac fly, Peter Kozma made it a 5-1 game with a single. Wainwright hit into a double play to end the frame.
St. Louis continued to pour it on in the second. With men on second and third, Matt Holliday grounded out to score one. Craig then singled in another run and Molina blasted a shot over the left-center wall, his 22nd of the season, for a 9-1 lead.
Bernadina hit a long homer to center in the seventh, his fifth of the year, for a 9-2 contest.
Matt Carpenter's RBI double in the eighth was followed by a homer from Robinson to extend the lead to 12-2.
Washington leads the season series, 3-2 ... The Nationals left eight men on base ... Wainwright moved to 4-3 in his career against Washington ... LaRoche has 99 RBI on the season.