Brendan Gibbons kicked two field goals and missed two one was blocked in OT for the Wolverines (5-1, 1-1). Sam Ficken kicked two, and didn't need to attempt a fourth, thanks to fourth-and-1 conversion by Penn State on what proved to be the game's final series.
The Nittany Lions (4-2, 1-1 Big Ten) stormed the field in wild celebration, sending more than 100,000 fans into a frenzy.
Still recovering from scandal, the Nittany Lions gave 107,884 fans at Beaver Stadium at long last a milestone celebration in Happy Valley. The Nittany Lions mobbed O'Brien, and he led the charge toward the students in the stands to sing the fight song. Penn State's victory bell rang long after the players had stunned the unbeaten Wolverines.
Hackenberg made it possible with plenty of help from his receivers on the final drive of the fourth.
Only a freshman, the 18-year-old Hackenberg played with the poise of a veteran, never more evident than in the final quarter.
Robinson expanded his 6-foot-3 frame about another 4 inches on a fantastic, outstretched leap in the corner that sent him crashing down a yard from the goal line. Lined up against a stout rushing defense, O'Brien called for the sneak, and Hackenberg plowed through for one sweet yard.
Hackenberg threw three touchdown passes in the first half to stake Penn State to a 21-10 lead.
After throwing two interceptions and losing a fumble in the first half, Devin Gardner put the Wolverines ahead with touchdown passes in the third and fourth quarters.
Helped by a pass interference call on third down that kept the drive alive, Gardner connected with Jeremy Gallon for a 16-yard TD pass for a 27-24 lead with 28 seconds left in the third.
Hackenberg overthrew a pair of open receivers on the deep ball and Ficken's tying 47-yard attempt was wide left early in the fourth.
Gardner needed only five plays to hit Devin Funchess in the back of the end zone for a 37-yard TD and a 34-24 lead.
Ficken hit a 43-yarder with 6:35 left to make it 34-27, keeping Hackenberg and the Nittany Lions alive for one thrilling finish.
This was a scene in Happy Valley straight out of the Joe Paterno era not like the late Hall of Fame coach has ever been forgotten. His picture is still on billboards that line the road to the stadium and T-shirts with his image or name were still a popular choice for fans.
But make no mistake. This program firmly belongs to O'Brien.
O'Brien hasn't backed down from a challenge since he took over the scandal-ridden program, and the Wolverines were the latest speed bump he flattened in his path.