ROSEMONT, ILL. ? Illinois made a jaw-dropping final push for the Final Four with a rally that was as electrifying as it was improbable.

“Just amazing,” Illinois coach Bruce Weber said.

Trailing by 15 with just four minutes to play Saturday night, the Illini finally showed why they had been No. 1 for most of the season.

“We just kept fighting. We never gave up,” Deron Williams said. “It looked like the game was over.”

But it wasn’t.

With Williams and Luther Head leading the way, Illinois went on a dazzling 20-5 run, tying it on Williams’ three-pointer, and then held on in overtime to send Arizona to a crushing 90-89 defeat Saturday night in the Chicago Regional finals.

“We’ve got to keep going, keep playing. I’m trying to tell my teammates out on the floor, ‘This game’s not over,'” Williams said. “‘There’s still some time, we can still get it down, chip away.’ We ended up getting the momentum, the crowd into it and we were able to take the game over.”

The Illini (36-1), who’ve been able to drive to their two tournament sites in Indianapolis and suburban Chicago, can keep on busing to the school’s first Final Four appearance since 1989.

In St. Louis, they will play Louisville (33-4), which rallied from a 20-point deficit Saturday to beat West Virginia, 93-85 in overtime, and take the Albuquerque Regional.

Illinois forward Roger Powell celebrates a 90-89 victory over Arizona in the championship game of the Chicago Regional. Trailing 75-60 with four minutes left, the Illini rallied for an overtime victory Saturday in Rosemont, Ill., and a trip to the Final Four in St. Louis.

The last time two regional final games went into overtime in the same year was 1992 when Michigan beat Ohio State, and Duke eliminated Kentucky.

Arizona (30-7) went up 75-60 with four minutes to go after an 18-6 spurt that momentarily silenced a large, orange-clad partisan crowd.

The Illini stoked up their defense, incited the crowd and turned the game around.

“It’s heart man, it’s just heart,” Illinois’ Dee Brown said. “The whole time I was saying ‘If it was meant to be, it was meant to be.’ And I guess it was meant to be that we go to the Final Four.”

Head hit a pair of three-pointers, Brown made a basket in the lane, Head scored after a steal, Williams drove for a basket and then made a steal and fed Brown for another basket with 45 seconds left.

After Jack Ingram deflected an inbounds pass, Williams hit a three-pointer to tie it with 38 seconds to go.

“Guys left and right on their team were hitting big buckets, left and right, left and right. Whether it was a big guy or a guard,” Arizona’s Mustafa Shakur said.

“It was just an unbelievable thing to lose a game that way.”

Even Weber, who was drawing up the defense to spark the comeback, couldn’t keep track of all that happened.

“It was just crazy,” he said. “We picked up the pace, did a little 2-2-1 zone, denied. Jack made a steal, Dee made a steal, and I’m not sure how Deron got the last three,” Weber said.

After Williams tied it at 80 in regulation, Salim Stoudamire, the hero of Arizona’s semifinal victory over Oklahoma State with a last-second game-winner, dribbled the clock down and then passed the ball to Jawann McClellan. He missed, but Stoudamire came up with a loose ball, only to have his shot blocked by Head.

“The defense collapsed on me. So I wasn’t going to force it, so I kicked it out to Jawann,” said Stoudamire, who managed just nine points under heavy defense from Williams.

Williams hit two more three-pointers in overtime, but Illinois’ victory wasn’t secured until Arizona’s Hassan Adams, who’d scored five points to get the Wildcats within a point, missed a rushed shot just before the final buzzer.

Arizona's Jawann McClellan sits on the court as Illinois' Dee Brown (11) and teammates celebrate their 90-89 overtime victory. The No. 1-seeded Illini rallied to win the NCAA Chicago Regional championship game Saturday at Allstate Arena in Rosemont, Ill.

Adams couldn’t get the ball inside to Channing Frye or drive, so he took the shot. But it wasn’t close.

“It’s extremely hard. … My disappointment is for the team,” Arizona coach Lute Olson said. “I’m disappointed we didn’t reach one of our goals. I wish we could have closed it out.”

Williams, a junior who might leave for the NBA, finished with 22 points, hitting five three-pointers, and had 10 assists. Head, playing despite a sore hamstring, added 20.

“We just played very hard down the stretch,” Brown said. “Deron Williams, the best guard in America, came through, made a lot of great plays. In the huddle we just said we aren’t going to lose this game.”

Stoudamire had a miserable game, making just two of 13 shots — 1-of-7 on three-pointers — and his chance of going to the Final Four for the first time as a senior was erased.

“It was just an off night on my part. I didn’t knock the shots down,” he said. “I didn’t quit, though. I tried to do other things on the floor, and it just so happens that we came up short.”

Frye was a force all night and finished with 24 points, 12 rebounds and six blocked shots. His three-pointer with 6:03 left was the last field goal the Wildcats scored in regulation.

Adams scored 21 on 9-of-13 shooting.