Iowa is stumbling at the wrong time.
Two months ago, the 24th-ranked Hawkeyes looked like a Big Ten title contender. Saturday night they lost for the fifth time in six games.
Jon Ekey hit a 3-pointer in the final second to lift Illinois to a 66-63 victory over Iowa (20-11, 9-9 Big Ten).
"I think we're a little bit fragile," Iowa coach Fran McCaffery said. "I think that's safe to say."
Rayvonte Rice scored 15 points to lead the Illini (18-13, 7-11 Big Ten), who notched consecutive road wins against ranked opponents for the first time since 2005.
Iowa's Roy Devyn Marble — the Big Ten's leading scorer — was held to eight points on 3-of-11 shooting.
A foul on Iowa's Mike Gesell with 13.8 seconds remaining reset the shot clock and gave Illinois the final shot.
On the final play, Illinois' Tracy Abram dribbled down the final seconds at top of the key. Abram first looked to Rice, but when he was covered the ball kicked out to Ekey.
Ekey drained the 30-foot game-winner over the outstretched arm of 6-foot-9 Aaron White with only a half-second on the game clock. Iowa's desperation heave from the baseline was picked off.
"It felt good," Ekey said of the release. "They switched it. They guarded it well."
Illinois ended the Hawkeyes' 30-game home winning streak against unranked opponents.
Ekey, who finished with 12 points, hit another big 3-pointer with 3:03 left to give the Illini a 63-59 lead.
The Hawkeyes misfired on their next few trips. Gesell missed a 3-pointer, Adam Woodbury threw away the ball and White mishandled a pass.
Marble — the only player in the Big Ten to score in double figures in every game before Saturday — had scored at least 20 points in each of the last five games.
"They weren't doing anything that they haven't done recently," McCaffery said of the defense. "It wasn't anything special other than they were keeping everybody in front of him to take away his penetration."
Illinois split the season series with Iowa despite 13 turnovers that led to 23 points for the Hawkeyes. The Illini were coming off a home loss to No. 12 Michigan on Tuesday, but had beaten then No. 18 Michigan State in East Lansing on March 1.
"We're playing the best we've played all year on both ends," Illinois coach John Groce said. "You want to have momentum and you want to be playing well."
Iowa is 15-4 this season when making at least five 3-pointers.
Illinois trailed most of the second half before Joseph Bertrand's jumper gave the Illini a 55-54 lead with 8:37 left.
The Hawkeyes tied it up twice after that, but never regained the lead.
Nnanna Egwu had 14 points and six rebounds for Illinois.
White led Iowa with 12 points and eight rebounds, and Woodbury added 11 points.
Iowa dug out of an early deficit with a 17-1 run in the first half.
Illinois opened the game with a 20-6 lead after scoring on eight of its first 10 possessions against the Hawkeyes' zone. Then McCaffery shifted to a smaller, quicker lineup and the Hawkeyes turned up the defensive intensity with tight man-to-man pressure.
Illinois went nearly eight minutes without a field goal as Iowa took a 23-21 lead.
"That was as good as defense as we've played," McCaffery said. "But that was the only good defense we played."
Almost all of that first-half spurt came without Marble, who picked up an early second foul and played only nine minutes in the first half.
The Hawkeyes honored seniors Marble, Melsahn Basabe, Zach McCabe and Darius Stokes on the floor before the game.
McCabe set a school record by playing in his 134th game.