EVANSTON, Ill. -- Clayton Thorson threw for two touchdowns after the end of regulation to help Northwestern upset 16th-ranked Michigan State 39-31 in triple overtime Saturday at Ryan Field.

It is the Wildcats' highest-ranked victory since defeating No. 10 Nebraska 28-25 on Nov. 5, 2011.

Thorson, who went 33 of 48 for 356 yards, found Flynn Nagel for a 22-yard touchdown in the third overtime period, then connected with Cameron Green on the two-point conversion attempt.

On the ensuring Michigan State drive, quarterback Brian Lewerke fumbled the ball but managed to recover it and roll out of the pocket, only to launch a prayer into the end zone. Northwestern linebacker Nate Hall intercepted the pass for the final play of the game.

Lewerke completed 39 of 57 passes to set career highs in yards (445) and touchdowns (four), including a 13-yard scoring strike to Felton Davis Jr. with 25 seconds remaining in regulation. Davis finished with eight catches for 95 yards and two touchdowns.

Northwestern coach Pat Fitzgerald praised Thorson's poise under pressure.

"He had pretty good football awareness in the pocket when there was pressure," Fitzgerald said. "As a quarterback, you're the hero, or you're the zero. That's what you sign up for. He had, I thought, a great game. I really thought he took what the defense gave him."

Nagel's go-ahead touchdown catch was only his second score of the season. His eight catches for 87 yards were both team highs and career highs. Nagel said Northwestern wanted to beat the Spartans through the air.

"That was part of the game plan, because they stacked the box and were trying to take away Justin (Jackson) like teams do, so I think we had to beat them through the air," Nagel said. "On the perimeter, we just did a better job separating. That helped us, obviously."

Jackson finished with 17 carries for 41 yards and touchdown, and he also threw a 12-yard touchdown pass to Bennett Skowronek to give Northwestern a 17-10 lead, capping a run of 17 unanswered points by the Wildcats.

Michigan State (6-2, 4-1 Big Ten) marched 92 yards in seven plays on its opening drive following a holding penalty on the opening kickoff. The Spartans capped the drive with a 6-yard touchdown pass from Lewerke to Cody White, whose 60-yard grab three plays earlier pushed the team into Northwestern territory. White finished with nine catches for a team-best 165 yards and two touchdowns -- all career highs.

Northwestern (5-3, 3-2) had not surrendered an opening-drive score in its first seven games.

"It's extremely disappointing, but credit Northwestern and the game they played," Michigan State coach Mark Dantonio said.

"We left points off the board. We missed two field goals hitting the bar. So, those are inches. We didn't find the inches. We had, I think, three shots downfield where we're inches away from making the play."

Matt Coghlin's 46-yard field goal extended Michigan State's lead to 10-0 with 9:31 remaining in the first half. Coghlin would miss field goal attempts from 51 yards and 32 yards in the second half, which proved costly down the stretch.

Northwestern's offense eventually got in sync, exploding for 130 yards in the second quarter and scoring twice in the final four minutes of the first half. Thorson capped a 13-play, 81-yard drive with a 1-yard touchdown run on fourth-and-goal at the 3:52 mark, and Charlie Kuhbander's 35-yard field goal with three seconds remaining tied the game at 10.

The Spartans had their eyes on a 5-0 start to conference play, which has happened only three times in school history. Instead, the Wildcats' rally earned them their third consecutive Big Ten victory after an 0-2 start to conference play.

Despite the loss, Michigan State outgained the Wildcats 445 to 368 and won the time of possession battle 34:59 to 25:01.

"Our football team played with conviction," Dantonio said. "They played with energy, they played with emotion, they played with intensity, and they never stopped playing throughout the entire time. That's all I can ever ask."

NOTES: Northwestern has converted 29 of 31 red zone attempts this season (93.5 percent). The Wildcats entered the game with a 92.3 percent red zone conversion rate, which ranked 15th nationally. ... Michigan State is bowl eligible for the 10th time in 11 seasons under Mark Dantonio. ... Northwestern has not played in back-to-back overtime games since 2007. The Wildcats defeated Iowa 17-10 in overtime last Saturday. ... Fraternal twins Andrew and David Dowell forced and recovered a fumble in the first half. LB Andrew forced the fumble, and S David recovered it. ... Michigan State entered the game as the top-ranked defense in the Big Ten by yards allowed. The Spartans had surrendered an average of 262.3 yards per game.