D'Agostini rifled a shot off the crossbar and into the net at the end of a 3-on-1 St. Louis break with 4 minutes left in the game, and the Blues went on to break a four-game road losing streak.
David Backes also scored and Halak turned aside 30-of-31 Florida shots, including 11 in the second period, while raising his season's record to 18-16-5 in his first appearance since the all-star break.
Dennis Wideman scored for the Panthers and Tomas Vokoun stopped 26-of-28 shots in losing to the Blues for the first time in 10 games.
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