Posted by ESPN.com's Adam Rittenberg

Penn State has had its share of close calls at Ryan Field, and for three quarters, Saturday's game seemed destined to be another one.

But the Nittany Lions took advantage of matchup advantages on both sides of the ball to wear down a scrappy Northwestern team playing without starting quarterback Mike Kafka. Penn State exploded in the fourth quarter and pulled away for a comfortable 34-13 win.

Senior quarterback Daryll Clark had another efficient performance and wore down a banged-up Northwestern secondary as wide receiver Derek Moye had a big performance. Big plays fueled Penn State's fourth-quarter surge, as Moye and running back Evan Royster broke free.

Credit Northwestern for hanging tough, but the Wildcats are simply too injured this season and couldn't do much on offense without Kafka, the Big Ten's passing leader. Penn State's defense prevented big plays and shut down the run, and Northwestern's defense couldn't hold a 13-10 halftime lead. The Wildcats had only two yards in the third quarter.

The surging Lions now face Ohio State in what looked like the Big Ten's premier game before the season. Northwestern tries to end Iowa's undefeated season.