Blues captain David Backes scored off a rebound during a power play 10:58 into overtime and St. Louis beat the Dallas Stars 4-3 in Game 2 on Sunday to get even in the second-round series.
St. Louis was on its second power play of overtime after Antoine Roussel was called for interference.
Vladimir Tarasenko took a slap shot that defenseman Alex Goligoski blocked. But the Blues kept charging and Backes scored on the rebound of Alexander Steen's shot.
The series matching the Western Conference's top two teams switches to St. Louis for Game 3 on Tuesday night.
Antti Niemi had stopped 19 consecutive shots since relieving Kari Lehtonen after the first period until Backes scored.
Blues goalie Brian Elliott had 31 saves.