IOWA CITY, Iowa -- With Ricky Stanzi watching from the sideline on crutches, No. 8 Iowa ran out of magic.

Dan Persa threw a touchdown pass and Marshall Thomas recovered a fumble for another score, and Northwestern dealt a crushing blow to Iowa's national championship hopes with a 17-10 victory Saturday.

Stanzi was knocked out of the game with an ankle injury in the second quarter on the play in which Thomas scored the Wildcats' first touchdown.

"Anytime you lose your quarterback, that's not good," Iowa coach Kirk Ferentz said.

The Hawkeyes (9-1, 5-1 Big Ten) have been living dangerously all season, making a habit of comebacks and close games. Still, they were good enough to be fourth in the latest BCS standings, hoping that with a slip or two by Florida, Alabama and Texas they could end up in the BCS Championship Game in Pasadena, Calif., on Jan. 7.

Now that their 13-game winning streak -- second longest in the nation -- has been snapped, the Hawkeyes' focus can shift to the other big game in Pasadena. Iowa can still win the Big Ten and land in the Rose Bowl on Jan. 1 for the first time since the 1990 season.

It was the first win over a top-10 opponent for the Wildcats (6-4, 3-3 Big Ten) since knocking off No. 6 Ohio State 33-27 in overtime in 2004.

Ferentz said Stanzi had a "severe" ankle injury. Freshman James Vandenberg was just 9 of 27 for 82 yards and couldn't lead the Hawkeyes to any points after Stanzi left the game.

Ferentz said that while preliminary X-rays on Stanzi's ankle were negative, he will likely be out the next couple of weeks. That's not a good sign for the Hawkeyes heading into next week's game against Ohio State in Columbus. Iowa finishes up at home against Minnesota.

"Right now we just have to take the approach that he won't go, and if he does that's a bonus," Ferentz said.

Northwestern scored twice off turnovers in the second quarter. Thomas' fumble recovery made it 10-7. Drake Dunsmore caught a 4-yard touchdown pass from Persa after another Iowa miscue.

Brandon Wegher had 63 yards rushing for Iowa. Stanzi was 4 of 9 for 134 yards with a touchdown, an interception and that costly fumble. Iowa committed four turnovers.

"It's hard to win football games against good, competitive teams, and that's basically everybody in our conference, if you're going to turn the ball over," Ferentz said. "If you do that week in, week out, you're not going to win many football games. That's what has allowed us to be successful. We have to get back to that formula."

Vandenberg, a native of Keokuk, Iowa, who holds the state high school record for career touchdown passes, had thrown three passes entering the game.

His inexperience showed and after the Hawkeyes won four games by three points or fewer this season they finally had a hole too deep to climb out.

Northwestern's Stefan Demos hit a 47-yard field goal with 13:29 left to give the Wildcats a 17-10 lead. The Hawkeyes had a chance to tie the game after taking over with 2:04 left on their own 17, but an incomplete pass on fourth down sent the Northwestern bench erupting in celebration.

Stanzi watched from the sideline in a warmup suit with crutches. He was taken to the locker room after being drilled in the end zone by Corey Wootton with 11:46 to go in the second quarter.

"Obviously it was a big momentum play. Not only get the sack to cause a fumble but you also get the touchdown," Northwestern coach Pat Fitzgerald said of the hit that knocked out Stanzi. "It was greatly important from a momentum standpoint."

Vandenberg's first pass was intercepted by Quentin Davie, and Northwestern took advantage. Persa's TD pass to Dunsmore gave the Wildcats their first lead, 14-10.

This was a huge win for Northwestern, which just last week got drilled by Penn State 34-13. Starting quarterback Mike Kafka left that game with a hamstring injury, and he and Persa split the snaps before Persa left in the third quarter with an apparent hand injury.

Before the injury to Stanzi, it looked like the Hawkeyes might finally have an easy game. They needed three plays for Stanzi to find Marvin McNutt for a 74-yard touchdown catch to make it 7-0, and Murray's 39-yard field goal pushed the lead to 10 midway through the first quarter.

But a week after committing six turnovers in a win over Indiana, Iowa turned it over four times in the second quarter against the Wildcats. Northwestern took its 14-10 lead despite gaining just 109 yards of offense in the first half.

The Hawkeyes honored former coach Forest Evashevski, who died last week at the age of 91, with a helmet decal and highlights on the scoreboard. Evashevski coached at Iowa from 1952-60, leading the Hawkeyes to three Big Ten titles and two wins in the Rose Bowl.

These Hawkeyes still control their Rose Bowl hopes.

"There's no time to hang our heads," Vandenberg said. "We're in a race with two other good teams and it's all going to be about getting back to work."