The hat trick was Legwand's first. Martin Erat, J.P. Dumont and Kimmo Timonen also scored for Nashville.
Martin Havlat, Craig MacDonald and Duncan Keith scored for Chicago.
The first period was a flurry of scoring. Nashville started it off when Legwand shot the puck across the goal mouth from the left side and Erat put it in off Nikolai Khabibulin's left pad at 7:14.
Twenty seconds later, Dumont gave Nashville a 2-0 lead when he beat Khabibulin to the glove side.
Chicago answered with a pair of goals.
Havlat scored on the power play at 9:37 when he took a wrist shot from low in the right circle.
Nine seconds later the game was tied when Mason wandered away from the net to make a pass. MacDonald got control of the puck above the right circle and fired a one-timer into an open net.