D'Agostini tucked in the rebound of his own shot 8:54 into the middle period to break a 1-1 tie, and the Blues held on to record a victory in Hunter's first game behind the Capitals' bench.
T.J. Oshie erased a 1-0 deficit with a tally late in the first period for the streaking Blues, who improved to 8-1-2 since their own coaching change that saw Ken Hitchcock take the reins.
Jaroslav Halak needed to make only 18 saves against the sluggish Capitals, who showed little jump for their new coach.
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