EVANSTON, Ill. -- Jack Mitchell was 0-for-2 on field goal tries and missed an extra point on Saturday.

Northwestern coach Pat Fitzgerald had no qualms about sending Mitchell out one more time.

The junior kicker made amends as he calmly split the uprights with a 35-yard game-winning field goal with nine seconds remaining as No. 21 Northwestern toppled Penn State 23-21 at Ryan Field.

"I have great confidence in Jack," Fitzgerald said. "Our plan was once we got inside the 33 we were going to kick the field goal to win. It looked like he put a great strike on that one."

Mitchell had earlier failed on 39 and 47-yard tries, but also knew how to deliver with games on the line, including a game-winner last year against Notre Dame.

"You try not to let yourself get down at all, even though you're not doing well," Mitchell said. "Fitz was telling me the whole game that you're going to be coming up big for us at the end of the game."

Northwestern backup quarterback Zack Oliver threw for one touchdown, rushed for another and went 11-of-24 for 111 yards after entering late in the second quarter in place of injured starter Clayton Thorson.

Running back Justin Jackson rushed 28 times for a career-high 186 yards as the Wildcats (7-2, 3-2 Big Ten) won their second straight.

Running back Saquon Barkley scored on runs of seven and 13 yards as Penn State (7-3, 4-2 Big Ten) rallied from a 20-7 third quarter deficit to a temporary 21-20 lead.

"They were able to run the ball on us consistently really all day long," Nittany Lions coach James Franklin. "On special teams, it's hard to give up a kickoff return for a touchdown and be successful."

Thorson left the game with lower body injury late in the first quarter. Oliver, a senior, worked the rest of the way in his fourth appearance of the year.

Oliver broke the shutout on the Wildcats' fifth possession with a 14-yard touchdown strike to wide receiver Christian Jones with 12:56 left in the first half.

Northwestern made it 13-0 on Oliver's one-yard keeper with 6:00 left in the half. Jackson helped set up the score with runs of 48 and 25 yards in a 5-play 91-yard drive.

Penn State tried the deficit to 13-7 with 2:18 left in the half when Barkley took the snap on a first and goal and scrambled seven yards for a touchdown.

The Wildcats quickly replied, opening a 20-7 lead with Solomon Vault's 96-yard kickoff return for a touchdown. It was Vault's second return TD of the season and third career, a school record.

Penn State took advantage of a pair of Northwestern personal fouls to keep a third quarter drive alive. Wide receiver Geno Lewis then lofted a 21-yard touchdown pass to wide receiver DaeSean Hamilton as the Nittany Lions trimmed the deficit to 20-14.

Northwestern had 396 yards total offense and a lopsided advantage on the ground. The Wildcats 227 rushing yards were 102 more than the Nittany Lions.

"At the end we had opportunities, four minute offense, four minute defense," Franklin said. "At the end, we weren't able to play winning football."

NOTES: Northwestern broke ground on Friday for a lakefront multipurpose indoor facility that will include space for football, Olympic team sports and recreational activities. ... The Wildcats were the Big Ten's least penalized team (4.50 per game) but had seven called for 80 yards on Saturday. ... Despite departing with a second quarter injury, dual threat QB Clayton Thorson is second on the team in rushing (410 yards) and tops in rushing touchdowns (five). ... A fourth quarter sack by Penn State DE Carl Nassib gave him a school record 15 1/2 for the season. The Nittany Lions have a bye week before closing the season at home against No. 17 Michigan and at No. 7 Michigan State.