Lehtonen gave up a lone goal in each of his first two appearances and has stopped 113-of-117 shots this season. He was not in goal for the only Dallas loss.
Matt D'Agostini scored for the Blues 20 seconds after Morrow's goal and Chris Stewart put a slap shot past Lehtonen 3:58 into the third.
Jaroslav Halak saved 21-of-24 shots for the Blues, who played on the road for the first time this season and lost for the second time in three games.
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