Dekker, last year's "Mr. Basketball" in the state of Wisconsin, gave the Badgers the lead for good with under two minutes remaining in the second overtime with his shot, which helped cap off a wild contest.
The Badgers led by as many as 11 in the first half, only to watch Iowa come all the way back and take a nine point lead of its own in the second half.
Traevon Jackson, another freshman, hit a three pointer to tie the game with 20 seconds left in regulation to help send the game to overtime.
Dekker's three pointer was Wisconsin's only field goal in either overtime session.
With the win, Wisconsin improves to 16-7 overall, 7-3 in the Big Ten. The Badgers welcome #3 ranked Michigan to the Kohl Center on Saturday.