Duckworth's 36-yard reception on a fourth-down, desperation heave by Russell Wilson gave the Badgers the ball 7 yards from a go-ahead score with 3:45 left in the inaugural Big Ten championship game.
Montee Ball followed with a TD run on the next play, handing Wisconsin (11-2) its second straight conference title and another trip to the Rose Bowl, where it will face Oregon.
The drive was kept alive when the Spartans' Isaiah Lewis was penalized for running into the kicker on a Badgers punt, which Keshawn Martin had returned to inside the Wisconsin 10-yard line.
Wilson tossed three touchdown passes and compiled 187 passing yards, while Ball ran rambled for 137 yards and three scores.
Kirk Cousins went 22-of-30 through the air for 281 yards, hitting B.J. Cunningham with three TD passes for the Spartans (10-3).
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