Left-hander Dallas Keuchel wasn't effective pitching on three days of rest for just the third time in his career.
The former Cy Young Award winner last pitched Thursday in Game 1, throwing just 74 pitches in the series opener.
Manager Brian Snitker indicated Sunday night that Keuchel was an option to start Game 4 but said he wanted to wait until Monday to make his final decision.
St. Louis got off to a fast start, delighting the crowd of 42,203 on a picturesque October afternoon. Paul Goldschmidt drove a 3-1 changeup from Keuchel deep to left with two out in the first, and Marcell Ozuna followed with a laser into the second deck in left for a 2-0 lead.
The Braves took a 2-1 series lead Sunday with a 3-1 victory in Game 3, highlighted by a dramatic three-run ninth-inning rally, but the series became all tied up at 2-2 when Cardinals catcher Yadier Molina hit a winning sacrifice fly in the 10th inning Monday.
Keuchel, 31, pitched 4 2/3 innings and did not record a decision in Atlanta's Game 1 loss, allowing one run and five hits with three walks and no strikeouts.
The two-time All-Star is 4-2 with a 3.20 ERA in 11 career postseason games, including 10 starts.
ESPN's Jesse Rogers and The Associated Press contributed to this report.