Posted by ESPN.com's Adam Rittenberg

IOWA CITY, Iowa -- Derrell Johnson-Koulianos had forgotten what it felt like to have someone other than Ricky Stanzi calling signals at the line of scrimmage.

	AP Photo/Charlie Neibergall
	Ricky Stanzi's injured ankle may keep him out of the rest of Iowa's regular-season games.

Johnson-Koulianos also had forgotten what it felt like to lose.

Unfortunately for the Iowa wide receiver, he experienced both sentiments Saturday against Northwestern. And he won't forget either feeling any time soon.

The fourth-ranked Hawkeyes lost their quest for perfection Saturday, unable to summon enough magic without Stanzi as they fell 17-10 to Northwestern at Kinnick Stadium.

"That was always in the back of my mind, something I really wanted for everybody," Johnson-Koulianos said of going undefeated. "It's never been done here. We had the opportunity to do something prestigious.

"Now that dream, in a blink of an eye, is gone."

Iowa lost its undefeated season, its quarterback and possibly the inside track to the Rose Bowl on Saturday. The Hawkeyes saw their 13-game win streak, the second-longest in the nation, snapped before a stunned crowd of 70,585, thousands of whom remained in their seats long after the game ended.

The margin for error had always been slim at Iowa, both on the field and the depth chart. Until Saturday, the Hawkeyes had overcome every challenge, from losing running backs Jewel Hampton and Adam Robinson, to playing several games without left tackle Bryan Bulaga and tight end Tony Moeaki, to facing eight deficits in nine weeks.

But the loss of Stanzi to a right ankle sprain in the second quarter proved too big an obstacle.

"There's no doubt that we're a different team when Rick Stanzi's in there," Johnson-Koulianos said. "We had a gift in Ricky, and there's going to be a huge drop-off [behind him]. His ability to make plays in critical situations, we knew that. We hadn't experienced life without him so far. We didn't know what to expect, and it resulted in a loss."

Life without Stanzi likely will continue for Iowa, as head coach Kirk Ferentz said the quarterback likely will miss Iowa's final two regular-season games. Iowa will put its faith in redshirt freshman quarterback James Vandenberg, who saw his first meaningful action of the season Saturday.

Vandenberg's first pass attempt in a Big Ten game was intercepted by Northwestern's Quentin Davie, leading to the go-ahead touchdown. Vandenberg finished the game just 9-for-27 passing for 82 yards.

"Relief pitcher who hasn't been in the majors long enough," Ferentz said of Vandenberg's arrival. "That's his first time out there, basically. It's a tough circumstance."

Most top-5 teams boast enough lopsided wins to get the backup on the field, but Iowa's season-long edge-of-the-cliff dance kept Vandenberg on the bench for all but one game. Vandenberg felt prepared Saturday and knew he'd be going in as soon as Stanzi went down, but the game brought different challenges.

"It's definitely faster, and the stakes are a lot more painful," he said.

Iowa didn't condense the playbook for Vandenberg, and the offense nearly pulled off several big plays. But Northwestern's defense buckled down, particularly in the fourth quarter, when Iowa never crossed midfield.

"They were giving me great time and the receivers were working really hard, but I made some mistakes that I shouldn't make," Vandenberg said.

He'll have a week to correct those mistakes before facing a top-10 defense next week in Columbus, a place where Iowa hasn't won since 1991. The young quarterback will need help from a Hawkeyes defense that held Northwestern to 10 points Saturday. He'll also need help from a running game that produced only 65 yards Saturday.

Iowa's top goal is off the table, but a Big Ten title remains within reach, and linebacker Pat Angerer tried to keep things in perspective.

"It hurts, but we've got two games left," Angerer said. "Worse things could happen. We're not at war. We live in a good country, we're going to school for free, we're living the American dream. We lost a football game. It's pretty small when you think of the big picture."

And if there's any team that can respond from a setback like this one, it's Iowa.

"This is another challenge we have," safety Joe Conklin said. "We've been down in games and come back, but you know what? This is our first loss. We've got our first taste of defeat. And no one in that locker room likes it."