It took away the Cardinals' ability to win their way to the playoffs without requiring help from others, putting them into a more precarious spot for the regular season's final six days.
St. Louis (81-75) enters the Tuesday night matchup with Cincinnati a game behind the San Francisco Giants (82-74) for the National League's second wild-card spot. The Cardinals are 1 1/2 games behind the New York Mets (83-74) for the top wild-card position, thanks to New York's 7-3 loss at Miami on Monday.
"You never want to be embarrassed, and that's an embarrassing loss," Cardinals managed Mike Matheny said of the 13-run defeat in the series opener.
About the only positive spin Matheny could generate from the team's worst loss of 2016 was that he got to rest some players. Catcher Yadier Molina played only four innings, while outfielders Randal Grichuk and Stephen Piscotty were excused after five.
"The key is to let it go and get back in there and show a different product tomorrow," Matheny said. "This team's done a very good job of that. It was just one of those days, but they all hurt to lose."
St. Louis will turn to Adam Wainwright (12-9, 4.57 ERA) in an attempt to right the ship. The veteran right-hander is coming off a 10-5 win on Sept. 20 in Colorado, where he allowed four runs over 5 1/3 innings. He also did major damage with his bat, driving in four runs to give him 18 RBI in 58 at-bats.
Wainwright hasn't enjoyed much success against the Reds this year, though, going 0-1 with a 6.06 ERA in three starts. In his career against Cincinnati, Wainwright is just 8-10 with a 4.41 ERA.
He will be opposed by rookie right-hander Robert Stephenson (2-2, 5.59 ERA), who was tagged for eight hits and four runs over 3 2/3 innings Wednesday night in a 9-2 loss at the Chicago Cubs. Stephenson will face the Cardinals for the first time.
Cincinnati (66-90) enjoyed perhaps its best game of the year Monday night, banging out 22 hits in a game for the first time since 2003 and notching a season high in runs. Along the way, a gaggle of Reds achieved significant milestones.
Left fielder Adam Duvall tallied single-game career highs with four hits, four runs and five RBI. He reached 100 RBI for the first time in his career with a three-run homer in the fifth -- his second of the game.
That Duvall has 33 homers and 100 RBI is significant. Not only was he playing his first full major league season after coming to Cincinnati last July from San Francisco, but he was expected to be a platoon outfielder.
"Phenomenal," Reds manager Bryan Price said of Duvall's season. "It's a huge accomplishment to hit 30 homers and drive in 100 runs, and make the All-Star team. It's hard to be really good for 162 games, but even when his offense has suffered, he's never let it affect his defense."