Without Stanzi, who sustained a severely sprained right ankle early in the second quarter, the Iowa offense sputtered.

Northwestern countered by playing a nearly error-free game for a 17-10 Big Ten victory at Kinnick Stadium in front of a crowd of 70,585.

"My guess is he'll be out of action here the next couple of weeks," Iowa coach Kirk Ferentz said of Stanzi, the erratic quarterback who typically steadies himself for late-game plays that have been a hallmark for this Iowa team.

Team spokesman Phil Haddy said a more definite prognosis could come Monday.

Northwestern snapped Iowa's 13-game winning streak that dated to last year. It was Northwestern's first win against a ranked team since 2004 and its first road win against a ranked team since 2000. Northwestern has won three consecutive games at Kinnick Stadium.

Iowa slipped to 9-1 (5-1 in the Big Ten) and remains in contention for a Rose Bowl berth. The Hawkeyes will play at No. 12 Ohio State next weekend.

"It hurts real bad, but you have to get it out of your mind," Iowa receiver Marvin McNutt said of the loss. "You just have got to get ready for O-State."

Northwestern (6-4, 3-3) came back from a 10-0 first-quarter deficit behind defensive end Corey Wootton, who sacked Stanzi in the end zone and forced a fumble that was recovered by Northwestern's Marshall Thomas for a touchdown.

"It was a big momentum play, not only to get the sack but to get the touchdown," Northwestern coach Pat Fitzgerald said.

Stanzi landed awkwardly on that play. As stunned Iowa fans watched, he limped off the field. Preliminary X-ray results were negative for a break, Ferentz said. Stanzi went 4-for-9 for 134 yards with a touchdown and an interception.

Stanzi returned later to offer words of wisdom to his replacement, redshirt freshman James Vandenberg. Before Saturday, Vandenberg had played in one game — against Iowa State — and completed two of three passes for 38 yards.

"Rick is our leader," McNutt said. "(Without him) some guys might have felt that things weren't clicking as well as they would have been."

On his first pass, Vandenberg threw an interception that set up a scoring drive for Northwestern.

Northwestern backup quarterback Dan Persa engineered that 10-play, 46-yard drive in the second quarter that culminated in a 4-yard touchdown pass to Drake Dunsmore.

Persa filled in for Mike Kafka, who started in spite of a hamstring injury. Persa injured a hand in the second half, and Kafka finished the game. Kafka went 10-for-18 for 72 yards; Persa went 5-of-9 for 37 yards. He threw one interception.

The Hawkeyes were shut out in the last three quarters, and Northwestern steered clear of turnovers that would have given Iowa room for a comeback.

"We're starting to play our best football of the year," Fitzgerald said. "We're starting to hit our stride."

Enlarge By Charlie Neibergall, AP Northwestern's Marshall Thomas, center, celebrates with teammates David Arnold, left, and Jack DiNardo after recovering a fumble in the end zone for a Wildcats score.