Beutjer tossed a 36-yard touchdown pass to Lewis to give Illinois (4-6, 3-3 Big Ten) the lead for good at 10-3 with just under three minutes to go in the first quarter. Lewis also hauled in a seven-yard scoring pass 49 seconds into the second quarter to make it 17-3.
Beutjer completed 22 of 34 passes for 319 yards and four touchdowns, including strikes to Walter Young and fullback Jason Davis. Young's 22-yard touchdown catch just before halftime gave Illinois a 24-13 lead.
But Beutjer also threw three interceptions as part of the Fighting Illini's five turnovers. Wisconsin strong safety Jim Leonhard returned his second interception of Beutjer 55 yards to the Illini 10-yard-line and Dwayne Smith scored on a one-yard plunge to cut the Badgers' deficit to 24-20 with 9:26 left in the third quarter.
Peter Christofilakos booted a 29-yard field goal for Illinois and Davis added a 12-yard touchdown reception. John Gockman added a 46-yard field goal to cap the scoring for the Illini.
Wisconsin (6-5, 1-5) still needs a win at Michigan or at home against Minnesota to become bowl eligible. Smith rushed for 122 yards on 22 carries with two touchdowns.