The Cardinals have played in three games that have gone 20 innings or more, with the most recent coming on April 17, 2010 vs. the New York Mets. The Cardinals lost that game, which went 6 hours and 53 minutes, and unless they can rally back from three runs down in the bottom half of the 19th, they will lose this one too.
Even if the Cardinals come back to tie, there would still be a long way to go before this game approaches the longest game in Cards' history. On Sep. 11, 1974, the Cardinals beat the Mets in a 25-inning marathon that lasted for over seven hours. The Cards had 99 plate appearances in that contest, and scored just four runs. Better than the Mets, at least, as they sent 105 batters to the plate and came away with only three.