The win ended a five-game losing streak for the Hoosiers (3-5, 1/3 Big Ten) that included tight losses to Ohio State, Navy and Michigan State. It also ended an 11-game Big Ten drought that dated to 2010.
Sudfeld took over after starting quarterback Cameron Coffman was benched following a first-quarter interception. His second scoring pass, a 17-yarder to Shane Wynn midway through the fourth quarter, put the Hoosiers up 31-17 and finished Illinois.
The Illini (2-6, 0-4) were led by Donovonn Young's career-high 124 rushing yards. Illinois has lost five in a row.
Saturday was homecoming for Illinois, but as Memorial Stadium emptied, the Hoosiers did all of the celebrating. The team gathered in the southeast corner of the stadium with a few dozen red-clad fans who likely shared the team's relief in finally getting a win.
Indiana's Big Ten losing streak dated to October 2010, and this season's losing skid included painful near-misses against Ohio State -- 52-49 two weeks ago -- and Navy. The Hoosiers looked to have last weekend's 31-30 loss to Navy in hand until almost the end.
This week, the defense earned its share of the win.
Indiana entered the game with just 12 sacks in seven games. But on Saturday, Illinois quarterback Nathan Scheelhaase scrambled for his own safety. Scheelhaase finished 12 of 27 for 176 yards and was sacked seven times.
The last sack sealed the win. Down 31-17, Illinois stayed alive with a drive to the Hoosiers 4 with just over 2 minutes to play. On first down, defensive end Ryan Phillis punched through the Illinois line and put Scheelhaase on his back for an 11-yard loss. The Illini came no closer to the end zone and Indiana took over with nothing to do but drain the clock.
Sudfeld wasn't asked to do much more than manage the game. He finished with 107 yards on 10-of-15 passing.
But his efficiency -- combined with key Illinois mistakes -- pulled the Hoosiers from a 14-7 deficit to a second-quarter lead they never gave up.
Illinois went up 14-7 early in the second on a 5-yard touchdown run by Scheelhaase and were set to stick Indiana with a three-and-out on the next series before Justin Staples was called for a late hit out of bounds on a third-and-3 play at the Hoosier 33. Sudfeld wasted no time, hitting Cody Latimer deep over the middle on the next play for 48 yards and a first-and-goal at the Illinois 6.
Two plays later, Stephen Houston took a screen pass from Sudfeld and dove into the end zone, squeezing just inside the right pylon. With the point after, the Hoosiers tied it at 14.
Indiana soon took its first lead on a pair of tough-to-justify mistakes by Illinois.
The first was return man Tommy Davis' puzzling decision to sprint across the field to try to field a Nick Stoner punt that was angling out of bounds. The diving Davis got a hand on the ball as he went out of bounds, leaving it for Indiana's Greg Heban to recover at the Illinois 22.
Three plays later, on third down, the Hoosiers used a long count to pull Illinois defensive tackle Glenn Foster offside, setting up a first-and goal at the 7. On the next play, Houston breezed around the left end for a touchdown and a 21-14 Indiana lead.
Illinois had eight penalties for 81 yards.
The penalties, sacks and turnovers were costly. The Illini had one of their best rushing days of the season with 196 yards, and had 23 first downs to Indiana's 14.
Indiana returns home to face Iowa next weekend, while the Illini will look for a way to end their losing streak at Ohio State.