Manager Mike Shildt and the Cardinals began the day with a one-game lead over Milwaukee but used Jack Flaherty's arm and Matt Carpenter's bat to ensure there would be no need for a division tiebreaker game Monday.
Flaherty pitched seven impressive innings, and Carpenter led a three-homer attack with a three-run drive to help St. Louis advance to the NL Division Series, starting Thursday at Atlanta.
"This is what it's all about,'' Shildt said. "I love to see the guys enjoy the fruits of their labor -- it's something special."
Paul Goldschmidt and Dexter Fowler also homered Sunday for St. Louis, which is back in the postseason after a three-year absence. The Cardinals have won or shared 12 division titles since the current format was developed in 1995.
"My fondest memories in baseball are the celebrations," said Goldschmidt, who was acquired in a trade from Arizona last December. "To accomplish this goal as a team, it's great. But we have to keep going.''
St. Louis (91-71) finished three games better than last season (88-74) as Shildt became the first manager in over a century to reach the postseason without ever having played in the major or minor leagues. The only others to do so were Pants Rowland of the 1917 Chicago White Sox and Ed Barrow of the 1918 Boston Red Sox.
Milwaukee's remarkable September ultimately fell two games short of stealing the division title following Sunday evening's 4-3 loss at Colorado. The Brewers (89-73) were only three games over .500 entering the month but proceeded to go 20-4 entering the final weekend to put a scare into St. Louis.
However, they were swept in their last series, against the lowly Rockies, and will now try to recover with their season on the line in a single game at Washington.
Manager Craig Counsell declined to say who would start for the matchup against Max Scherzer and the Nationals.
A sellout crowd of 47,212 in St. Louis watched Sunday's contest, pushing the Cardinals' attendance to 3,480,393, an average of 42,968 per game. It marked the 22nd sellout of the season. St. Louis averaged 42,020 last season.
As has become tradition over the years, the fans sang the national anthem prior to the last home game of the season without the help of an organ.
Information from The Associated Press was used in this report.