Gasser also grabbed eight rebounds and Jared Berggren contributed 12 points for the Badgers (23-8, 12-6 Big Ten), who won four out their final five Big Ten Conference games.
Ryan Evans chipped in with 10 for Wisconsin, which will go into this week's conference tourney with a first-round bye.
The Illini (17-14, 6-12) couldn't translate Brandon Paul's 22 points into a win, instead falling for the eighth time in nine contests.
Meyers Leonard grabbed 12 rebounds for Illinois, which has the ninth seed in post-season play.
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