The Stars tested coach Jim Montgomery's patience in the first period on Monday by giving St. Louis another power-play chance.
The opportunity arose when Jamie Benn was called for tripping on Colton Parayko. As has been the case throughout the postseason, the Stars kept the Blues from scoring.
Montgomery is concerned about a penalty-killing group that is pressing its luck. The Stars kept the Blues from scoring on five chances Saturday.
A team cannot continue to do that and keep winning, Montgomery said.
"That's why our discipline needs to improve,'' Montgomery said. "We were excellent against Nashville, and we haven't maintained our emotional control as well as we should in this series so far.