Lunt was 35 of 50 with one interception for the Illini (2-0).
Barton picked off Hilltopper quarterback Brandon Doughty in the fourth quarter for a 77-yard touchdown that put Illinois up 35-27.
Illinois trailed 17-7 late in the second quarter on a 16-yard touchdown pass from Doughty to tight end Tyler Higbee.
Western Kentucky (1-1) went ahead again in the third quarter on a 95-yard fumble return by cornerback Wonderful Terry
Hilltopper running back Leon Allen finished with 118 yards on 24 carries and a touchdown. Doughty was 28 of 48 for 297 yards, a touchdown and the interception.
Illinois wide receiver Justin Hardee caught six balls for 110 yards and one touchdown.