After a scoreless first period, PSU forged a 10-0 halftime advantage, which grew to 17-0 on Royster's 4-yard scoring run with 8:02 left in the third quarter.
The Nittany Lions improved to 6-0 (2-0 Big Ten) on a day when longtime Coach Joe Paterno watched from the press box because of an ongoing right hip injury.
Nittany Lion quarterback Darryl Clark ran for one touchdown and passed for 220 yards, while placekicker Kevin Kelly booted two field goals.
PSU had lost four of its previous five road contests.
Purdue's Kory Sheets scored on a 1-yard, fourth-quarter run and finished with 59 yards on 18 carries.
The Boilermakers (2-3, 0-1) scored their first touchdown in the last three games against the Nittany Lions.
Placekicker Chris Summers missed two field goals and an extra point try.