Instead, they ran into Chicago's buzzsaw — Jake Arrieta.
Arrieta (10-5), coming off a one-hit shutout against Cincinnati last week, limited St. Louis to two hits and an unearned run while striking out 10 in seven innings, leading the Cubs to a 3-1 victory.
"He's got swing-and-miss stuff in the strike zone and he's got the ability to get it out of the strike zone as well, and that makes him tough," Cardinals infielder Matt Carpenter said. "Anytime you got a guy with that type of electric stuff, you kind of feel like you're on defense up there. Anytime he gets ahead of you, you're in a bad spot."
Arrieta outdueled St. Louis' John Lackey (3-3), both on the mound and at the plate. After Lackey intentionally walked Logan Watkins in the fourth inning, Arrieta hit a two-run triple — the first triple of his career and the first by a Cubs pitcher since 2012. The Cubs never surrendered the lead.
"It's amazing that that at-bat is the one that does it," Cardinals manager Mike Matheny said.
Lackey gave up two runs and five hits in 6 2-3 innings. He struck out eight, his most since joining the Cardinals at the trade deadline.
The Cardinals, who clinched a playoff berth earlier in the week, remained 1 1/2 games ahead of Pittsburgh in the NL Central. The Pirates lost at Atlanta, reducing St. Louis' magic number to three for clinching the division title.
"I'm tired of looking up there and waiting for somebody else to help us," Matheny said following the game. "Nobody's helped us all season long. Why are they going to start now?"
The Cardinals' loss assured NL East champion Washington will open a division series at home.
The Cardinals were held without a hit through four innings but managed two singles in the fifth. Yadier Molina came in to score on Welington Castillo's throwing error, cutting the Cubs lead to 2-1.
Molina has hit safely in seven consecutive games and 12 of his past 14.
Chris Valaika had a pinch-hit RBI single in the eighth to extend the Cubs lead to 3-1.
The Cardinals mounted a two-out rally in the ninth, but Hector Rondon worked out of the jam for his 13th consecutive save and his 27th in 31 opportunities this season.
After the game, Arrieta took pride in playing the role of spoiler.
"To pitch well against them, at this time of the season with the implications on the game that are there, it's meaningful," Arrieta said. "It's just another positive thing to use moving forward into the offseason."
Arrieta has allowed two or fewer runs in 19 of 25 starts this season.
Cubs: SS Starlin Castro will miss the remainder of the season, according to manager Rick Renteria. Castro injured his left ankle sliding into home against the Milwaukee Brewers on Sept. 2.
Cardinals: OF Jon Jay missed Wednesday's game due to a personal matter. He will rejoin the team on Friday in Arizona.
Cubs: LHP Eric Jokisch (0-0, 1.74) will make his first career start on Friday when the Cubs open a three-game set at Milwaukee.
Cardinals: RHP Michael Wacha (5-6, 3.18), who missed approximated three months earlier this season with a stress reaction in his throwing shoulder, starts for the Cardinals on Friday against Arizona.
Now that the Cubs' regular-season schedule is over, improvements and renovations at the 100-year-old ballpark — including constructing a large video scoreboard in left field — are expected to begin soon. The scoreboard and other outfield signs are expected to be in place by the start of next season, but the new home clubhouse isn't slated to be completed until 2016.