The Blackhawks (39-18-5) improved to 9-1-0 in their past 10 games and have 83 points, one behind the Minnesota Wild for the top spot in the Central Division and Western Conference.
WATCH: All Blackhawks vs. Blues highlights
"It's really encouraging watching the team the last few weeks getting cohesion going at this point in the season," said Darling, who started for Corey Crawford (illness). "We're very confident in our team, and that's the way you want to be. You want to be excited to get going at this point in the season, leading into the playoffs and get that good feeling in the room. We're excited about the way we're playing."
Jonathan Toews and Patrick Kane scored Chicago's first two goals for a 2-0 lead in the first period, but St. Louis tied it 2-2 on goals by Magnus Paajarvi at 16:54 of the first and Alex Pietrangelo at 12:33 of the second.
Jake Allen made 38 saves for the Blues (31-25-5), who lost their third straight game and remain four points behind the Nashville Predators for third in the Central. It was the first game following the break for St. Louis.
"We were right there," Allen said. "We fought our way back in the game and it's a tough one to swallow again. We've got to find ways to get even a point out of these games right now. They're so crucial."