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STATE COLLEGE, Pa. -- With his team a little stunned after giving up a 75-yard punt return for a touchdown, Penn State coach Bill O'Brien walked up and down the sideline giving players a pep talk.

After everything they've been through over the past year, these Nittany Lions weren't going to be denied, even after trailing by 11 going into the fourth quarter.

Quarterback Matt McGloin had the go-ahead score on a 5-yard touchdown run with 2:37 left, one of three fourth-quarter scores for Penn State, and the Nittany Lions stormed past No. 24 Northwestern 39-28 on Saturday.

"Our staff and myself, we tried to talk to the players and get them going," O'Brien said. "We felt like we could move the ball."

And how.

The Nittany Lions (4-2, 2-0 Big Ten) scored three times in the final 9:49, starting with McGloin's 6-yard touchdown pass to Allen Robinson on fourth down as the receiver dragged along the back line of the end zone. Michael Zordich had a 2-point conversion run to get Penn State within 28-25 before McGloin's scramble for a score sent the homecoming weekend crowd into a frenzy.

"Nobody's down. There's no quit in that locker room," O'Brien said. "I don't know what's going to happen the rest of the year, but there will be no quit in that locker room."

The Nittany Lions then stuffed Northwestern's last-gasp drive after Trevor Siemian's pass for Kain Colter was tipped away on fourth down. Zordich added a 3-yard touchdown run with 1:30 left to put a punctuation mark on the wild finish.

Things looked so good for Northwestern (5-1, 1-1) after Venric Mark's 75-yard punt return for a touchdown with 50 seconds left in the third quarter demoralized the blue-and-white faithful for a 28-17 lead.

Mark also ran for a score and finished with 72 yards on 13 carries.

The Wildcats couldn't get to 6-0 for the first time in 50 years. Even worse for Northwestern, the loss continued a disturbing trend of second-half collapses against Penn State. The Wildcats had halftime leads the previous two years before falling to the Nittany Lions.

This year, they couldn't hang on to an 11-point lead in the fourth quarter.

"It was tough," safety Ibraheim Campbell said about the last 15 minutes. "We've just got to find a way to make a play. Guys were out there for a while. The offense was out there the same as us. We've just got to find a way to focus in, make a play and get off the field."

Some of it couldn't be helped given the way Penn State kept going for it on fourth down, including Robinson's second touchdown catch of the game. Penn State was an astounding 5 of 6 on fourth-down conversions on the day.

"I didn't think twice about it," O'Brien said. "You've got to make the touchdown. You've got to make the play."

Adding to his reputation as a bold play-caller, O'Brien then decided to go for two. Zordich rumbled up the middle to get the Nittany Lions within three.

It's certainly a new era for the Penn State offense if nothing else. Under late head coach Joe Paterno, the Nittany Lions were known more for the running game and playing for field position.

But the defense, with a few tweaks, remains a hallmark in Happy Valley.

After bending in the middle of the game against Northwestern's high-octane spread, Linebacker U. didn't break in the fourth. Dual-threat quarterback Kain Colter found his running lanes filled with swarming defenders, and defensive backs smothered the receivers.

Linebacker Gerald Hodges led the charge with 11 tackles and a forced fumble.

McGloin struggled at times, too, but bounced back in the clutch. McGloin directed blockers in front of him as he rolled right but couldn't find a receiver. So the savvy senior just got into the front corner of the end zone for the touchdown.

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McGloin finished 35 of 51 passing -- setting a school record for completions in a game -- for 282 yards and two scores. Zack Zwinak ran for 121 yards and a score on 28 carries.

A week after dismantling Indiana for 704 yards of total offense, Northwestern hit a speed bump in Happy Valley. The Wildcats were outgained 443-247 in total offense and 30-14 in first downs.

Northwestern was also 4 of 14 on third- and fourth-down plays, while Penn State was 15 of 28.

"That's a recipe for disaster. We're on the field way too long. We're not sustaining drives," Northwestern coach Pat Fitzgerald said. "Our recipe is exactly what they did for success. We got beat at our own game."

Yet they still were in a good spot in the third quarter after Colter had a 10-yard scoring run with 3:12 left before Mark's terrific punt return touchdown about two minutes later for a 28-17 lead.

Colter, who had nearly 300 yards of total offense last week, was held to five carriers for 24 yards and three catches for 17 yards. Robinson finished with nine receptions for 85 yards and two touchdowns.