Eight different hitters knocked in runs for St. Louis (76-68), led by three from Yadier Molina. Tommy Pham, Paul DeJong and Jose Martinez added two RBIs each, with DeJong cracking his 22nd homer of the year in the sixth.
Leadoff hitter Matt Carpenter set a career high by drawing walks in his first four plate appearances, then added an RBI double on his only official at-bat of the game in the seventh.
Lance Lynn (11-7) was the beneficiary of the support, winning for the first time since Aug. 3 - his last start against Cincinnati. Lynn lasted five innings, giving up six hits and four runs, three of them earned. He walked none and whiffed three.
The win enabled the Cardinals to stay within two games of the Cubs. They also pulled within three of Colorado for the NL's second wild-card spot, pending the outcome of the Rockies' game in Arizona.
It was St. Louis' 11th win in 14 games.
Robert Stephenson (4-5) was shelled for five hits and six runs (four earned) in three innings. He walked three and fanned five as he lost for the first time in six starts.
Five pitchers combined for nine walks, two wild pitches and an error for the Reds (62-83).
After Cincinnati's Zack Cozart belted a 433-foot shot over the Reds' bullpen in left-center field to initiate scoring in the top of the first, Yadier Molina laced a two-run, two-out double in the bottom of the first for St. Louis.
The Cardinals made it 5-1 in the second with more two-out work.
Tommy Pham lined a two-run triple to right-center, then trotted home on Paul DeJong's RBI double off the left-center field wall.
Randal Grichuk's sacrifice fly in the third upped the margin to 6-1. Jose Martinez joined the fun in the fourth with a two-run double down the left field line that increased the advantage to 8-1.
The Reds responded with three in the fifth. Adam Duvall produced an RBI single. Patrick Kivlehan tripled to right-center to score Duvall and then scored on a throwing error by pitcher Lance Lynn on Jesse Winker's comebacker.
NOTES: St. Louis recalled OF Magneuris Sierra from Triple-A Memphis and optioned INF Breyvic Valera to the Redbirds, who are in the PCL championship series. Sierra is 19-for-52 in 13 games with the Cardinals during two short stints earlier this year. ... Cincinnati reinstated OF Jesse Winker (left hip flexor) from the 10-day DL and recalled RHP Keury Melia from Double-A Pensacola. The Reds also selected the contract of RHP Deck McGuire from Pensacola. ... St. Louis RHP Adam Wainwright (right elbow) threw a bullpen session and will either repeat it on Thursday or face live hitters. Wainwright, 12-5 with a 5.12 ERA, has been on the 10-day DL since August 18.