Nigel Hayes scored 25 points, Frank Kaminsky added 19 and No. 6
Bronson Koenig scored 18 points, and the Badgers (31-3) rallied from 11 points down in the second half in an attempt to strengthen their bid for a No. 1 seed in the NCAA Tournament.
In the first overtime in a Big Ten title game, Hayes and Koenig hit 3-pointers in the first 3 minutes to give the Badgers a 75-69 lead. Michigan State missed all six shots and committed two turnovers in the extra period.
All that came after a wild finish in regulation.
Michigan State led 57-46 after going on a 17-5 run midway through the second half, only to have Wisconsin come back. The Badgers scored 11 straight in a 2-minute stretch and grabbed a 60-59 lead on Koenig's 3-pointer with 4:16 left.
Michigan State was up by two before Kaminsky scooped in a shot from the left block and hit a 3-pointer from NBA range to give Wisconsin a 67-64 lead with 1:44 left.
Valentine than quieted the Badgers fans with a tying 3 over Kaminsky, and Travis Trice drove down the right side for an off-balance floater to put Michigan State ahead 69-67 with 45 seconds remaining.
Koenig missed a 3 off the dribble after a timeout and the Badgers' John Gasser, trying to make a save in the corner, threw it to Valentine. Dekker then stole a bad pass from him, and Koenig hit two free throws to tie it at 69-all with 15 seconds remaining.