EVANSTON, Ill. — Evan Royster rushed for 118 yards, including a 69-yard touchdown during Penn State's fourth-quarter surge, and the 12th-ranked Nittany Lions blanked Northwestern in the second half of a 34-13 victory Saturday.

Daryll Clark threw a 53-yard TD pass to Derek Moye before Royster broke loose for the third of three Penn State touchdowns during a span 3 minutes, 40 seconds of the fourth quarter that turned a tight game into a rout.

Penn State (8-1 4-1 in the Big Ten) trailed 10-3 in the second quarter when Northwestern quarterback Mike Kafka was forced out with a leg injury. And the Nittany Lions were still behind 13-10 at the half. But they shut out the Wildcats and backup QB Dan Persa in the final two quarters and gave coach Joe Paterno his 391st win.

Behind the strong running of Royster, Penn State moved in for the go-ahead touchdown early in the final quarter on a 3-yard run by Brandon Beachum that made it 20-13.

When the Nittany Lions got the ball back, Clark rolled right and found Moye behind Northwestern's secondary for the 53-yard TD pass, making it 27-13 with 10:16 to go.

After Penn State forced another punt, Royster broke through the Northwestern defense on first down and sprinted to the end zone.

Northwestern (5-4, 2-3) finished with 371 yards total offense after having 246 in the first half.

Clark was 22 of 31 for 274 yards.

Kafka injured his leg midway through the second quarter. He'd been sacked and then completed a pass before he replaced by Persa.

After talking on the phone on the sideline, Kafka left for the locker room with just more than five minutes to go in the first half. He had completed 14 of 18 passes for 128 yards and carried eight times for 42 yards, helping Northwestern build a 10-3 lead.

He was on the sideline during the second half and even pedaled an exercise bike, but did not return. He entered the game leading the Big Ten in passing yards and total offense per game.

Clark led the Nittany Lions on a 93-yard drive in seven plays, going 5 for 5 for 64 yards and also carrying for 12 yards. After a pass interference call on Northwestern, Clark hit Curtis Drake for 13 yards and then scored from the 2 — his 20th career rushing TD, tying Michael Robinson's school record.

Persa then got the Wildcats in position for a go-ahead score but Jared Odrick blocked Stefan Demos' 37-yard field goal attempt. Demos got another shot and hit a 45-yarder with three seconds left in the half to give Northwestern the 13-10 lead.

Collin Wagner kicked a 23-yard field goal to tie it in the third quarter.

After the team's traded first-quarter field goals, Kafka and the Wildcats grabbed the lead in the second quarter.

Kafka completed four straight passes in a hurry-up offense, had a 13-yard keeper on a key third down, and carried the final 7 yards to complete an 80-yard TD drive that put Northwestern up 10-3. It was just the second first-half TD allowed by Penn State's rugged defense all season.

Penn State entered the game allowing the fewest points per game in the nation (8.9 points) and led the Big Ten in rushing, passing and total defense.