In the second round, Benn snapped a wrist shot that got between Backstrom's pads and Lehtonen made it hold up for the win with a stop on Jared Spurgeon.
Mike Ribeiro netted the Stars' only regulation goal and Lehtonen made 33 saves for Dallas, which pulled to within two points of Minnesota for the eighth and final Western Conference playoff spot.
The Wild lost for the sixth time in nine games, managing only a single goal from Kyle Brodziak.
Backstrom turned away 25 shots.
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