Dekker, a true freshman, scored his 19 points in 22 minutes off the bench. He was 5-6 from the field and 4-5 from 3-point range.
Ryan Evans added 14 points and 7 rebounds for Wisconsin, while Ben Brust was the other Badger player in double figures with 13.
With the win, the Badgers improved to 20-8 overall, 11-4 in the Big Ten. Wisconsin is now 1 game behind first-place Indiana, who lost Tuesday night to Minnesota. It's the seventh season in a row the Badgers have won 20 games or more.
Wisconsin has won its last three games by 20 or more points. It's the first time they've won three straight conference games by that margin since the 1911-1912 season.
The Badgers return to action Sunday afternoon, when they host Purdue at the Kohl Center.