Wildcats can't keep pace with Penn St.
Mike Kafka's hamstring injury knocked him out of Saturday's game midway through the second quarter.
But Northwestern didn't share the senior quarterback's pain until the fourth quarter.
The Wildcats and 12th-ranked Penn State played even through three quarters, but the Nittany Lions struck for 3 scores in a 3-minute, 30-second stretch to pull away for a 34-13 Big Ten triumph before 30,546 at Ryan Field.
Thus, for Northwestern's fourth conference game in a row, the team that owned the halftime lead didn't go home happy.
"Penn State took advantage of it when we didn't do our job and make plays," NU senior safety Brad Phillips said. "I feel like a broken record. Because that's what's been happening to us in games that we've been close and teams have taken advantage of us when we haven't done our job appropriately."
This game, of course, featured the additional twist (of the knife) of Kafka's injury.
After fumbling the ball away on the game's second snap, the Big Ten's leader in total offense had things clicking against the national leader in scoring defense (8.9 ppg).
When Kafka slashed in from 7 yards out to cap a swift 80-yard drive, Northwestern owned a 10-3 lead with 12:31 left in the first half.
But on the Wildcats' next possession, Kafka hurt his left hamstring without being touched as he stepped up in the pocket and juked past defensive tackle Devon Still.
He stuck it out for one more play before making way for redshirt sophomore Dan Persa, a Bethlehem, Pa., native whose mother and sister attended Penn State and influenced his rooting interests as a youth.
Initially, Persa looked like he might develop into a hometown non-hero in his first extended action against a Football Bowl Subdivision foe.
On Persa's first two drives, he directed NU (5-4, 2-3) into field-goal range. Stefan Demos nailed a 45-yarder just before halftime to give the hosts a 13-10 lead.
"I don't think we had quite realized how good they are offensively," Penn State coach Joe Paterno said, "and it took us some time to speed up the tempo."
The Nittany Lions offense sped up with it.
During the first 22 minutes of the second half - the stretch when the Nittany Lions (8-1, 4-1) made Paterno's 391st career win possible - Northwestern was outgained 271-39 as Persa did little with the limited time he had to make things happen.
"That doesn't really excuse the way I played," Persa said. "I didn't get it done."
With NU stymied, Penn State scored on three consecutive fourth-quarter snaps to turn a taut game into a rout.
After backup tailback Brandon Beachum's 2-yard run broke the tie with 12:27 to go, senior quarterback Daryll Clark threw a 53-yard play-action touchdown bomb to Derek Moye.
Then Clark faked a wide-receiver screen and handed off to starting tailback Evan Royster, who raced up the middle untouched for a 69-yard score.
"You've got to make plays: End of discussion," Fitzgerald said. "You want to win games? It's about big plays and execution and playing physical and doing it for 60 minutes."