Andrew Quarless and Graham Zug each caught two scoring passes from Clark.
Evan Royster gained 114 yards on 13 carries.
Quarless and Zug combined for 161 receiving yards.
The defense forced two key turnovers.
Derek Moye caught four passes for 99 yards, while Joe Suhey made four receptions for 56 yards for the Nittany Lions (10-2, 6-2), who lead the all-time series, 14-12-1.
MSU's Kirk Cousins completed 16-of-28 passes for 155 yards with one touchdown and two interceptions.
Edwin Baker was held to 48 yards on nine carries, and Charlie Gantt and Keshawn Martin each caught touchdown passes for the Spartans (6-6, 4-4), whose two-game winning streak ended.