CHAMPAIGN, Ill. — The plan was for Wisconsin to roll into a showdown with Ohio State unbeaten, with a defense putting up historic numbers and a Heisman Trophy contender at running back.

Illinois had other plans.

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James McCourt kicked a 39-yard field as time expired, and the Illini pulled off the biggest upset of the season, knocking off No. 6 Wisconsin 24-23 on Saturday.

"Our program, we needed to get a signature win. I was just hoping today was the day, and the day came," said Illini coach Lovie Smith, the former Chicago Bears coach who entered the game 11-31 overall and 4-26 in the Big Ten since taking over Illinois in 2016.

Tony Adams picked off a pass by Jack Coan for the Illini (3-4, 1-3 Big Ten), who were 30-point underdogs, at midfield with 2:33 remaining that set up the winning drive.

Dre Brown's tackle-breaking 13-yard run got Illinois (3-4, 1-3) to the Wisconsin 25 with 34 seconds left, and then the Illini set up McCourt to attempt a winner. The junior kicker was down the middle with the field goal to give Smith the most significant victory for Illinois in years.

"No matter if it's an extra point or a game-winner, you kind of have to take the approach that every kick is the same because if you take a different approach, you might get thrown off or something might be a little different," said McCourt, who missed a 40-yard attempt in the first quarter.

Fans rushed the field when it was over, and "Jump Around" — a signature song at Wisconsin's Camp Randall Stadium — blared through the speakers at Memorial Stadium.

The Badgers had not trailed this season, allowing 29 points with four shutouts in six games. Wisconsin (6-1, 4-1) blew a nine-point lead in the final 9:46 of the fourth quarter.

Heisman contender Jonathan Taylor rushed 28 times for 132 yards and one touchdown for Wisconsin, but he also lost a fumble in Illinois territory in the fourth quarter to help fuel the comeback.

"We had two drives late in the game that ended in turnovers," Wisconsin coach Paul Chryst said. "It's always hard to win on the road, and that made it even harder. We just have to move on and learn from this."

Coan was 24 of 32 passing for 264 yards and a touchdown, but his second turnover of the season came at a crucial time. He sailed a pass on third-and-5 that Adams grabbed to give the Illinois a short field against the No. 1 defense in the nation.

Illinois had cut Wisconsin's lead to 20-14 late in the third quarter on a 43-yard touchdown run by Reggie Corbin.

Wisconsin had opportunities to pad its lead but settled for a field goal after a first-and-goal from the 3, and then Taylor fumbled at the Illinois 25.

After the fumble, the Illini ripped off a 75-yard touchdown drive, capped by Brandon Peters' 29-yard pass to Josh Imatorbhebhe to make it 23-21 with 5:53 left.