The sophomore quarterback completed 13 of 21 passes for 161 yards and rushed for 81 yards on nine carries.
The Spartans (2-0) gained 296 yards on 49 rushing attempts.
Running back LJ Scott, who fumbled twice in Michigan State's 35-10 season-opening win over Bowling Green, had a rushing and receiving touchdown. Scott had a team-high 86 yards rushing on 18 carries and caught three passes for 25 yards.
Darius Phillips scored both of the Broncos' touchdowns on a fumble return and kickoff return. Jon Wassink completed 11 of 26 passes for 79 yards with an interception for the Broncos (0-2), who lost their opener to USC 49-31. LeVante Bellamy led the rushing attack with 67 yards on 12 carries,
Phillips' defensive touchdown with 8:43 remaining in the third ended Western Michigan's scoring drought. He stripped wide receiver Hunter Rison on an end around, then picked up the fumble and scampered 67 yards to cut the Spartans' lead to 14-7.
Michigan State responded quickly on Lewerke's 1-yard plunge with 6:07 left in the quarter. That score was immediately preceded by Darrell Stewart's 46-yard run.
Scott's 2-yard run with 10:48 remaining extended the Spartans' lead to 28-7. Scott's 44-yard run on a fourth-and-1 situation set up that score.
Phillips then returned the ensuing kickoff 100 yards for a touchdown.
The Spartans led 14-0 at halftime.
Lewerke used his quickness to put Michigan State on top. He faked a handoff, then cut left and outraced the defense on his 61-yard run with 4:43 remaining in the first quarter.
Lewerke found Scott along the left sideline on a 15-yard scoring pass with 6:04 left in the half to make it 14-0.
The Broncos were limited to 85 total yards and failed on all seven of their third-down conversion attempts during the half.