Trey Stross had 91 yards receiving and a touchdown for the Hawkeyes, who rallied from a 14-point deficit for the second straight week to win their third game in four tries.
With home games against Minnesota and Western Michigan remaining, Iowa (5-5, 3-4 Big Ten) needs just one more win to become bowl eligible.
The Wildcats, meanwhile, blew a chance of becoming bowl eligible for the second straight week. Northwestern led Purdue 17-14 after three quarters last week, but was outscored 21-0 in the fourth quarter.
Northwestern led 17-14 after three quarters yet again against Iowa, but was outscored 14-0 in the fourth this time.
Christensen's 53-yard pass to Stross down the left sideline set up a 2-yard touchdown run by Sims with 7:44 left, giving Iowa its first lead of the game, 21-17.
Northwestern (5-5, 2-4) had two chances to put it away, but C.J. Bacher threw interceptions on consecutive possessions -- one to Bradley Fletcher and the other to Charles Godfrey.
Godfrey's interception with 5:08 left led to Sims' second score, an 8-yard run that gave Iowa a 28-17 lead.
Bacher threw for 264 yards, a touchdown and three interceptions for the Wildcats. Tyrell Sutton added 116 yards rushing and a score.
The Hawkeyes trailed 14-0 after the first quarter -- getting outgained 196-11 -- but outscored Northwestern 28-3 the rest of the way to snap a two-game losing streak to the Wildcats.
After managing just 12 yards and no first downs in the first quarter, Iowa finally got a first down with 12:42 left in the second when Sherrick McManis was penalized for roughing the kicker on a Hawkeyes punt.
Iowa then scored for the first time late in the quarter, pulling within seven on Christensen's 20-yard touchdown pass to Stross with 49 seconds left.
Adrian Clayborn blocked a 34-yard Northwestern field-goal attempt in the closing seconds of the second quarter to keep the score 14-7.
Iowa then opened the second quarter with a 71-yard, 10-play drive to tie it at 14. Albert Young capped the drive with a 16-yard score, taking the handoff up the middle, juking toward a hole on the right and running untouched into the end zone.
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Steve Spurrier, the visor-slinging, slick-talking "Head Ball Coach" who is the second-winningest coach in Southeastern Conference history, announced his resignation on Tuesday.
USC athletic director Pat Haden spoke Tuesday about the decision to fire head coach Steve Sarkisian, calling it "very difficult," while also defending his handling of the situation.
Bevo XIV began his tenure at the age of 2 in 2004. He was a part of back-to-back Rose Bowl victories, including the January 2006 win that resulted in a BCS title.
Tennessee running back John Kelly was taken to the hospital as a precaution and released after getting hurt during the Volunteers' Tuesday afternoon practice.The injury was not specified.
Steve Sarkisian has been plagued of late by apparent substance-related circumstances, including arriving to team facilities appearing intoxicated Sunday, according to sources.
A former Texas A&M football recruit randomly attacked a jogger, using a "large-bladed knife" to repeatedly strike the man and lodging the weapon in his head, according to police documents.