EVANSTON, Ill. — Daryll Clark patiently probed Northwestern's defense until finally finding the openings Penn State had been seeking all game.

Erupting for three fourth-quarter touchdowns in less than four minutes, the 11th-ranked Nittany Lions pulled away for a 34-13 victory Saturday night that sends them into a showdown with Ohio State this week riding a five-game winning streak.

Clark rolled and threw a 53-yard TD pass to Derek Moye. And on the Nittany Lions' very next scrimmage play, Evan Royster ran through and past the Wildcat defense on a 69-yard score.

"For the whole game we took what they gave us. We noticed that there were a couple of voids in their defense. We knew there would be a big play for us," Clark said.

And so was Northwestern's chances for an upset. The Wildcats (5-4, 2-3 Big Ten) instead had their bowl chances severely damaged and now head to unbeaten Iowa.

Clark, who threw four TD passes against Michigan a week earlier, had his 20th career rushing touchdown, tying Michael Robinson's school record.