"The one thing Ayo has is 6-(foot)-5," Illinois coach Brad Underwood said.
Dosunmu took advantage of his 5-inch height edge on Simpson, sinking a contested jumper from the free throw line with 0.5 seconds remaining to give No. 21 Illinois a 64-62 victory over Michigan on Saturday. The Illini extended their winning streak to six and moved into sole possession of first place in the Big Ten for the moment.
"Simpson, he played great defense. He couldn't have guarded that any better," Dosunmu said. "But I just got into my pull-up, got into my moves, and then just knocked the shot down."
Illinois (15-5, 7-2) won despite a quiet game from freshman big man Kofi Cockburn, who fouled out after scoring five points with three rebounds. Michigan (11-8, 2-6) has dropped four in a row and may again be without forward Isaiah Livers because of an injury.
The Wolverines let the game slip away at the foul line, where they went 0 for 5 in the final four minutes. Illinois tied it at 62 on a pair of free throws by Trent Frazier with 52.3 seconds left. Then Jon Teske missed inside for Michigan, and the Illini had the ball back.
"Coach just said, `No ball screen," Dosunmu said. "He told me, just make sure I got the last shot. He believed I was going to make the right play."
Illinois was able to run the clock down and isolate Dosunmu -- who said his nickname was "Iso" in high school -- against Simpson. Dosunmu couldn't shake Simpson with a quick fake, but he was able to elevate and shoot over the Michigan guard.
"We tried everything. Great effort -- I don't think you can tell us that we didn't play hard today," Michigan's Franz Wagner said. "Free throws, a couple defensive lapses -- that's how you lose a game like that."
Michigan had one last possession with under a second left, but the Wolverines didn't get a shot off.
Dosunmu finished with 27 points.
Livers returned for Michigan after missing six games with a groin injury, but he left in the second half after hurting himself again. Livers was fouled during a dunk attempt -- the same way he got hurt the first time -- and came up holding his groin area. He did go back in at the very end to throw the long inbound pass for the Wolverines after Dosunmu's shot.
"His effort out there was great," said coach Juwan Howard, who said Livers is day to day. "Energy from the crowd when his name was called just shows how much he's a huge part of this team's success."
Simpson led Michigan with 17 points.
Illinois: It's been quite a run for the Illini, who won in Ann Arbor for the first time since 2010. Illinois was tied with Michigan State for first place entering the game. The Spartans have a chance to pull even again when they play Sunday.
Michigan: The Wolverines shot poorly to start the game and missed too many free throws late. They did a lot of other things right -- Michigan turned the ball over only twice and contained Illinois on the boards -- but this season is in danger of slipping away.
Michigan trailed 34-30 at halftime and did not have a single assist in the first half. The Wolverines were 1 for 11 from 3-point range in the half and finished 4 of 17 on the day.
Simpson had three of Michigan's five assists for the game.
"I think he's the leading assist guy in the country, and they have five assists as a team and none in the first half," Underwood said. "If you would have told me before the game that we're going to hold Michigan to five assists, I would have liked our chances."
This is Illinois' highest AP ranking since it was No. 12 in January 2013, and the Illini will probably move up after beating Purdue and Michigan this week.
Illinois: The Illini host Minnesota on Thursday night.
Michigan: The Wolverines travel to play Nebraska on Tuesday night.
Follow Noah Trister at https://twitter.com/noahtrister
More AP college basketball: https://apnews.com/Collegebasketball and https://twitter.com/AP-Top25
No. 17 West Virginia looks to salvage split of Texas trip
and remains -- one of the biggest issues surrounding the No. 17 Mountaineers as they head into Austin on Monday to square off against battered, but suddenly hot, Texas.
Cincinnati's Harvey drops in and-1 while falling down
Cincinnati guard Zach Harvey drives to the bucket and drops in an acrobatic layup while drawing a foul.
84-year-old woman sinks incredible putt, wins a car
At Ole Miss vs. Alabama, 84-year-old Mary Ann Wakefield sinks a full-court putt to win a car.